Why is there so much space before my array's first row? How can I fix it (as I don't believe that this is its default behaviour)?

\documentclass[12pt]{article}
\usepackage{parskip}
\setlength{\parindent}{0cm}
\usepackage{fontspec}
\usepackage[english,greek]{babel}
\usepackage[fleqn]{amsmath}
\usepackage{unicode-math}
\setmainfont
[
Ligatures=TeX,
Extension=.otf,
UprightFont=*,
BoldFont=*Bold,
ItalicFont=*It,
BoldItalicFont=*BoldIt,
Mapping=tex-text
]{GFSArtemisia}
\setsansfont[Mapping=tex-text]{GFSArtemisia.otf}
\setmathfont{latinmodern-math.otf}
\setmathfont[range=\varnothing]{Asana-Math.otf}
\setmathfont[range=\int]{latinmodern-math.otf}
\begin{document}
\begin{equation}
\left[\begin{array}{c c c}
g_{11} & g_{12} & g_{13}\\
g_{21} & g_{22} & g_{23}\\
g_{21} & g_{32} & g_{33}
\end{array}\right]
\end{equation}
\end{document}
The list of files (not from the MWE but from my normal preamble)
article.cls 2007/10/19 v1.4h Standard LaTeX document class
size12.clo 2007/10/19 v1.4h Standard LaTeX file (size option)
geometry.sty 2010/09/12 v5.6 Page Geometry
keyval.sty 1999/03/16 v1.13 key=value parser (DPC)
ifpdf.sty 2011/01/30 v2.3 Provides the ifpdf switch (HO)
ifvtex.sty 2010/03/01 v1.5 Detect VTeX and its facilities (HO)
ifxetex.sty 2010/09/12 v0.6 Provides ifxetex conditional
parskip.sty 2001/04/09 non-zero parskip adjustments
amsmath.sty 2013/01/14 v2.14 AMS math features
amstext.sty 2000/06/29 v2.01
amsgen.sty 1999/11/30 v2.0
amsbsy.sty 1999/11/29 v1.2d
amsopn.sty 1999/12/14 v2.01 operator names
unicode-math.sty 2013/05/04 v0.7e Unicode maths in XeLaTeX and LuaLaTeX
ifluatex.sty 2010/03/01 v1.3 Provides the ifluatex switch (HO)
expl3.sty 2014/01/07 v4646 L3 Experimental code bundle wrapper
l3names.sty 2014/01/04 v4640 L3 Namespace for primitives
l3bootstrap.sty 2014/01/04 v4640 L3 Experimental bootstrap code
etex.sty 1998/03/26 v2.0 eTeX basic definition package (PEB)
l3basics.sty 2014/01/04 v4642 L3 Basic definitions
l3expan.sty 2014/01/04 v4642 L3 Argument expansion
l3tl.sty 2013/12/27 v4625 L3 Token lists
l3seq.sty 2013/12/14 v4623 L3 Sequences and stacks
l3int.sty 2013/08/02 v4583 L3 Integers
l3quark.sty 2013/12/14 v4623 L3 Quarks
l3prg.sty 2014/01/04 v4642 L3 Control structures
l3clist.sty 2013/07/28 v4581 L3 Comma separated lists
l3token.sty 2013/08/25 v4587 L3 Experimental token manipulation
l3prop.sty 2013/12/14 v4623 L3 Property lists
l3msg.sty 2013/07/28 v4581 L3 Messages
l3file.sty 2013/10/13 v4596 L3 File and I/O operations
l3skip.sty 2013/07/28 v4581 L3 Dimensions and skips
l3keys.sty 2013/12/08 v4614 L3 Experimental key-value interfaces
l3fp.sty 2014/01/04 v4642 L3 Floating points
l3box.sty 2013/07/28 v4581 L3 Experimental boxes
l3coffins.sty 2013/12/14 v4624 L3 Coffin code layer
l3color.sty 2012/08/29 v4156 L3 Experimental color support
l3luatex.sty 2013/07/28 v4581 L3 Experimental LuaTeX-specific functions
l3candidates.sty 2014/01/06 v4643 L3 Experimental additions to l3kernel
xparse.sty 2013/12/31 v4634 L3 Experimental document command parser
l3keys2e.sty 2013/12/31 v4634 LaTeX2e option processing using LaTeX3 keys
fontspec.sty 2013/05/20 v2.3c Font selection for XeLaTeX and LuaLaTeX
fontspec-patches.sty 2013/05/20 v2.3c Font selection for XeLaTeX and LuaLaTeX
fixltx2e.sty 2006/09/13 v1.1m fixes to LaTeX
fontspec-xetex.sty 2013/05/20 v2.3c Font selection for XeLaTeX and LuaLaTeX
fontenc.sty
eu1enc.def 2010/05/27 v0.1h Experimental Unicode font encodings
eu1lmr.fd 2009/10/30 v1.6 Font defs for Latin Modern
xunicode.sty 2011/09/09 v0.981 provides access to latin accents and many
other characters in Unicode lower plane
eu1lmss.fd 2009/10/30 v1.6 Font defs for Latin Modern
graphicx.sty 1999/02/16 v1.0f Enhanced LaTeX Graphics (DPC,SPQR)
graphics.sty 2009/02/05 v1.0o Standard LaTeX Graphics (DPC,SPQR)
trig.sty 1999/03/16 v1.09 sin cos tan (DPC)
graphics.cfg 2010/04/23 v1.9 graphics configuration of TeX Live
xetex.def 2013/04/29 v0.96 LaTeX color/graphics driver for XeTeX (RRM/JK)
fontspec.cfg
catchfile.sty 2011/03/01 v1.6 Catch the contents of a file (HO)
infwarerr.sty 2010/04/08 v1.3 Providing info/warning/error messages (HO)
ltxcmds.sty 2011/11/09 v1.22 LaTeX kernel commands for general use (HO)
etexcmds.sty 2011/02/16 v1.5 Avoid name clashes with e-TeX commands (HO)
fix-cm.sty 2006/09/13 v1.1m fixes to LaTeX
ts1enc.def 2001/06/05 v3.0e (jk/car/fm) Standard LaTeX file
filehook.sty 2011/10/12 v0.5d Hooks for input files
unicode-math-xetex.sty
unicode-math-table.tex
babel.sty 2013/12/03 3.9h The Babel package
english.ldf 2012/08/20 v3.3p English support from the babel system
greek.ldf 2013/12/03 v1.8a Greek support for the babel system
greek-euenc.def 2013/12/02 0.11.1 Greek LICRs for XeTeX and LuaTeX
greek-fontenc.def 2013/11/28 v0.11 Common Greek font encoding definitions
xgreek-fixes.def
listings.sty 2013/08/26 1.5b (Carsten Heinz)
lstmisc.sty 2013/08/26 1.5b (Carsten Heinz)
listings.cfg 2013/08/26 1.5b listings configuration
multicol.sty 2011/06/27 v1.7a multicolumn formatting (FMi)
xcolor.sty 2007/01/21 v2.11 LaTeX color extensions (UK)
color.cfg 2007/01/18 v1.5 color configuration of teTeX/TeXLive
colortbl.sty 2012/02/13 v1.0a Color table columns (DPC)
array.sty 2008/09/09 v2.4c Tabular extension package (FMi)
dvipsnam.def 1999/02/16 v3.0i Driver-dependant file (DPC,SPQR)
svgnam.def 2007/01/21 v2.11 Predefined colors according to SVG 1.1 (UK)
longtable.sty 2004/02/01 v4.11 Multi-page Table package (DPC)
tikz.sty 2010/10/13 v2.10 (rcs-revision 1.76)
pgf.sty 2008/01/15 v2.10 (rcs-revision 1.12)
pgfrcs.sty 2010/10/25 v2.10 (rcs-revision 1.24)
everyshi.sty 2001/05/15 v3.00 EveryShipout Package (MS)
pgfrcs.code.tex
pgfcore.sty 2010/04/11 v2.10 (rcs-revision 1.7)
pgfsys.sty 2010/06/30 v2.10 (rcs-revision 1.37)
pgfsys.code.tex
pgfsyssoftpath.code.tex 2008/07/18 (rcs-revision 1.7)
pgfsysprotocol.code.tex 2006/10/16 (rcs-revision 1.4)
pgfcore.code.tex
pgfcomp-version-0-65.sty 2007/07/03 v2.10 (rcs-revision 1.7)
pgfcomp-version-1-18.sty 2007/07/23 v2.10 (rcs-revision 1.1)
pgffor.sty 2010/03/23 v2.10 (rcs-revision 1.18)
pgfkeys.sty
pgfkeys.code.tex
pgffor.code.tex
tikz.code.tex
t3cmr.fd 2001/12/31 TIPA font definitions
\listfilesto your preamble and then add the list that appears at the end of the log file to your question then people can see the version of all packages used – David Carlisle Jan 29 '15 at 19:53