Check if the game install directories exist before issueing the xcopy

command.  Cheap trick to make it so Steam and Oculus install locations can
be used.  People keep overwriting this setting.  If you use a non-standard
install dir, make a sym link to it at the standard install dir.

SongBrowserPlugin/SongBrowser.csproj

@@ -217,7 +217,8 @@
   <ItemGroup />
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
   <PropertyGroup>
-    <PostBuildEvent>xcopy "$(TargetDir)$(TargetFileName)" "C:\Program Files\Oculus\Software\Software\hyperbolic-magnetism-beat-saber\Plugins" /Y</PostBuildEvent>
+    <PostBuildEvent>IF EXIST "C:\Program Files\Oculus\Software\Software\hyperbolic-magnetism-beat-saber\Plugins" xcopy "$(TargetDir)$(TargetFileName)" "C:\Program Files\Oculus\Software\Software\hyperbolic-magnetism-beat-saber\Plugins" /Y
+IF EXIST "C:\Program Files (x86)\Steam\steamapps\common\Beat Saber\Plugins" xcopy "$(TargetDir)$(TargetFileName)" "C:\Program Files (x86)\Steam\steamapps\common\Beat Saber\Plugins" /Y</PostBuildEvent>
   </PropertyGroup>
   <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
          Other similar extension points exist, see Microsoft.Common.targets.