Another question about making the name of an author bold in the bibliography

Question

I'm using biblatex and wish to print a name (which has a "ä" character, say "Därwin") bold every time it shows up in the bibliography.

This answer provides a solution that works, provided my tex file is ISO-8859 encoded (I'm not sure I understand all the details about encoding). However, it ruins the detection of the last author in the list, whose name should be preceded by "and" and not followed by a comma. So instead of "Smith and Doe (1990)" I get "Smith, Doe, (1990)", even when the author printed in bold is Därwin.

Here's a MWE:

 \documentclass{article}
 \usepackage[latin9]{inputenc}

 \usepackage[style=authoryear-comp,natbib=true,%
 minbibnames=15,%
 maxbibnames=15,%
 backend=biber]{biblatex}
 \usepackage{filecontents}
 \begin{filecontents}{\jobname.bib}
 @Book{Darwin.84,
   author =      {C. D\"{a}rwin},
   title =   {The different forms of flowers on plants of the same species},
   publisher =   {John Murray},
   address =      {London},
   edition =      2,
   year =    1884}

 @ARTICLE{Davies.pnas04,
 AUTHOR = {Davies, T. J. AND Barraclough, T. G. AND Chase, M. W. AND Soltis, P. S. AND Soltis, D. E. AND Savolainen, V.},
 TITLE = {D\"{a}rwin's abominable mystery: {Insights} from a supertree of the angiosperms.},
 JOURNAL = {Proc. Natl. Acad. Sci. U.S.A.},
 VOLUME = {101},
 PAGES = {1904--1909},
 YEAR = {2004},
 MONTH = Feb,
 NUMBER = {7}
 }

 @ARTICLE{Vamosi.el10,
 AUTHOR = {Vamosi, J. C. AND Vamosi, S. M.},
 TITLE = {Key innovations within a geographical context in flowering plants: towards resolving {D\"{a}rwin}'s abominable mystery.},
 JOURNAL = {Ecol. Lett.},
 VOLUME = {13},
 PAGES = {1270--1279},
 YEAR = {2010},
 MONTH = Oct,
 NUMBER = {10}
 }


 \end{filecontents}
 \addbibresource{\jobname.bib}

 \newcommand{\makeauthorbold}[1]{%
 \DeclareNameFormat{author}{%
   \ifnumequal{\value{listcount}}{1}
     {\ifnumequal{\value{liststop}}{1}
       {\expandafter\ifstrequal{##1}{#1}{\textbf{##1\addcomma\addspace ##4\addcomma\isdot}}{##1\addcomma\addspace ##4\addcomma\isdot}}
       {\expandafter\ifstrequal{##1}{#1}{\textbf{##1\addcomma\addspace ##4}}{##1\addcomma\addspace ##4}}}
     {\ifnumless{\value{listcount}}{\value{liststop}}
       {\expandafter\ifstrequal{##1}{#1}{\textbf{\addcomma\addspace ##1\addcomma\addspace ##4}}{\addcomma\addspace ##1\addcomma\addspace ##4}}
       {\expandafter\ifstrequal{##1}{#1}{\textbf{\addcomma\addspace ##1\addcomma\addspace ##4\addcomma\isdot}}{\addcomma\addspace ##1\addcomma\addspace ##4\addcomma\isdot}}%
     }%
 }%
 }
 \makeauthorbold{Därwin}


 \makeatother

 \begin{document}

 Les \oe{}uvres de \citeauthor{Darwin.84} ont souvent été citées, par exemple par \citet{Davies.pnas04,Vamosi.el10}.


 \printbibliography

 \end{document}

It produces this output:

How to get "and Savolainen, V. (2004)" ?