Ungrab before animating when releasing a drag actor

Inside this._ungrabEvents() we ungrab the pointer or the touch sequence. Since touch sequences are no longer valid right after the touch i.e. the drag ended, we really shouldn't access them later after the snap-back animation finished.

Instead, simply ungrab the events before starting the animation to make sure the sequence ungrab happens either during the touchpoint is still on the screen or while handling a TOUCH_END event.