OSX: add another missing AutoReleasePool.

No leaks no cry.

Change-Id: Id44993f037447dd84e1ccd4d985877e7f57bb979
Reviewed-by: Morten Johan Sørvig <morten.sorvig@theqtcompany.com>

src/widgets/styles/qmacstyle_mac.mm

@@ -1753,6 +1753,7 @@ QMacStylePrivate::QMacStylePrivate()
 
 QMacStylePrivate::~QMacStylePrivate()
 {
+    AutoReleasePool pool;
     Q_FOREACH (NSView *b, cocoaControls)
         [b release];
 }