Installer should not hardcode the installdir path

This changes $INSTDIR to respect InstallDirRegKey. If not present, the default is the drive of %ProgramFiles% instead of forcing c:\.

Author: whindsaks

RosBE-Windows/RosBE.nsi

@@ -52,7 +52,12 @@ Function .onInit
  StrCmp $R0 0 +3
  MessageBox MB_OK|MB_ICONEXCLAMATION "The ${PRODUCT_NAME} v${PRODUCT_VERSION} installer is already running."
  Abort
- StrCpy $INSTDIR "C:\RosBE"
+
+ ${If} $INSTDIR == "" ; InstallDirRegKey not valid?
+ StrCpy $0 $ProgramFiles 1
+ StrCpy $INSTDIR "$0:\RosBE"
+ ${EndIf}
+
  Call UninstallPrevious
  !insertmacro INSTALLOPTIONS_EXTRACT "RosSourceDir.ini"
 FunctionEnd