WaE: case value not in enumerated type 'NSEventSubtype'

Change-Id: Iaf5de07b7f0da7294681b9cdc152575a756a73c7

vcl/osx/salinst.cxx

@@ -445,7 +445,8 @@ bool AquaSalInstance::isNSAppThread() const
 
 void AquaSalInstance::handleAppDefinedEvent( NSEvent* pEvent )
 {
-    switch( [pEvent subtype] )
+    int nSubtype = [pEvent subtype];
+    switch( nSubtype )
     {
     case AppStartTimerEvent:
         AquaSalTimer::handleStartTimerEvent( pEvent );