iOS: Don't try to set screen orientation before QApplication startup

We create our QIOSViewController in didFinishLaunchingWithOptions,
and schedule a timer to run the user's main. If the device is
placed in landscape orientation at startup, we will receive a
willRotateToInterfaceOrientation message before the timer is
triggered to run the user's main, which means we do not yet
have a QApplication.

To fix this crash we exit early, but we might have to store the
new orientation for later, and make sure the initial QScreen is
then created with the correct orientation.

Change-Id: I0cc02f0d36b992d190736e98858dc7d002d595b7
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>

src/plugins/platforms/ios/qiosviewcontroller.mm

@@ -78,6 +78,10 @@
 - (void)willRotateToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration
 {
     Q_UNUSED(duration);
+
+    if (!QCoreApplication::instance())
+        return; // FIXME: Store orientation for later (?)
+
     Qt::ScreenOrientation orientation = toQtScreenOrientation(UIDeviceOrientation(toInterfaceOrientation));
     if (orientation == -1)
         return;