QCoreTextFontDatabase: reduce memory consumption

ATSFontNotify() allocates over 30MB for no apparent reason for
applications that don't register fonts.

Change-Id: I7bbc97f53b76be1e638de8ca0d1be3a08586cf00
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@digia.com>
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>

src/platformsupport/fontdatabases/mac/qcoretextfontdatabase.mm

@@ -768,6 +768,9 @@ QList<int> QCoreTextFontDatabase::standardSizes() const
 
 void QCoreTextFontDatabase::removeApplicationFonts()
 {
+    if (m_applicationFonts.isEmpty())
+        return;
+
     foreach (const QVariant &font, m_applicationFonts) {
 #if HAVE_CORETEXT
         if (&CTFontManagerUnregisterGraphicsFont && &CTFontManagerUnregisterFontsForURL) {