iOS: animate screen from current in-flight geometry

If you show/hide the keyboard quickly while we scroll the
screen, the scroll will appear to jump. The reason is that
the screen animation will start from where the model layer
is at, and not the presentation layer. So specify that
the animation should start from the current state of the
presentation layer.

Change-Id: I3db87ab11aab583eb50784b0c0a03a9a07c8b822
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>

src/plugins/platforms/ios/qiosinputcontext.mm

@@ -329,7 +329,7 @@ void QIOSInputContext::scroll(int y)
     newBounds.origin.y = y;
     QPointer<QIOSInputContext> self = this;
     [UIView animateWithDuration:m_keyboardListener->m_duration delay:0
-        options:m_keyboardListener->m_curve
+        options:m_keyboardListener->m_curve | UIViewAnimationOptionBeginFromCurrentState
         animations:^{ view.bounds = newBounds; }
         completion:^(BOOL){
             if (self)