Cocoa: QCocoaApplicationDelegate - correctly install cleanup handler

+ (id)allocWithZone:(NSZone *)zone returns before the cleanup handler is
installed. this causes the QCocoaApplicationDelegate not to be cleaned up
by the garbage collector

Change-Id: Ic4862b96228539f3da857955f08157402974a104
Reviewed-by: Morten Johan Sørvig <morten.sorvig@theqtcompany.com>

src/plugins/platforms/cocoa/qcocoaapplicationdelegate.mm

@@ -131,8 +131,8 @@ QT_END_NAMESPACE
     @synchronized(self) {
         if (sharedCocoaApplicationDelegate == nil) {
             sharedCocoaApplicationDelegate = [super allocWithZone:zone];
-            return sharedCocoaApplicationDelegate;
             qAddPostRoutine(cleanupCocoaApplicationDelegate);
+            return sharedCocoaApplicationDelegate;
         }
     }
     return nil;