osgeo4w: don't register .qgs file extensions if release version is installed

(fixes OSGeo4W#415)

Author: jef-n

ms-windows/osgeo4w/postinstall-dev.bat

@@ -13,7 +13,8 @@ set OSGEO4W_ROOT=%OSGEO4W_ROOT:\=\\%
 textreplace -std -t "%O4W_ROOT%\apps\@package@\bin\qgis.reg"
 set OSGEO4W_ROOT=%O4W_ROOT%
 
-nircmd elevate "%WINDIR%\regedit" /s "%O4W_ROOT%\apps\@package@\bin\qgis.reg"
+REM Do not register extensions if release is installed
+if not exist "%O4W_ROOT%\apps\qgis\bin\qgis.reg" nircmd elevate "%WINDIR%\regedit" /s "%O4W_ROOT%\apps\@package@\bin\qgis.reg"
 
 call "%OSGEO4W_ROOT%"\bin\o4w_env.bat
 path %PATH%;%OSGEO4W_ROOT%\apps\@package@\bin