s0artcl: fix title font when titlepage is used

needs \xpatchcmd because \patchcmd cannot patch commands with optional
parameters, see xpatch package documentation

s0artcl.cls

@@ -28,7 +28,7 @@
 
 % --- Helper packages
 % ---
-\RequirePackage{etoolbox}
+\RequirePackage{xpatch}
 
 % --- Page Layout
 % ---
@@ -40,9 +40,11 @@
 % Yanone Kaffeesatz ZeroHack for titles etc.
 \RequirePackage{yanonekaffeesatzzerohack}
 \setkomafont{title}{\usefont{LY1}{YanoneKaffeesatzZeroHack}{b}{n}}
-% koma-script has an explicit \huge directly in \maketitle...
+% koma-script has an explicit \usekomafont{title}{\huge \@title}...
+% see http://tex.stackexchange.com/a/82851
 \makeatletter
-\patchcmd{\@maketitle}{\huge}{\fontsize{24pt}{32pt}\selectfont}{}{}
+\xpatchcmd{\maketitle}{\huge}{\Huge}{}{}
+\xpatchcmd{\@maketitle}{\huge}{\Huge}{}{}
 \makeatother
 \setkomafont{section}{%
 \fontsize{16pt}{24pt}\selectfont%

test.tex

-\documentclass{s0artcl}
+%\documentclass{s0artcl}
+\documentclass[titlepage]{s0artcl}
 \usepackage[utf8]{inputenc}
 
 \title{A Test Document for the Stratum~0 Corporate Design}