Android: fixed media player buffering logic.

When the media is ready, the status should always transition to
LoadedMedia and then immediately to BufferingMedia or BufferedMedia.
Also, when the duration is queried before the media is ready but already
buffering, it should always return 0 to avoid errors from the Android
media player.

Task-number: QTBUG-32635
Change-Id: Ibcb9c23b4f64c4f9a1a8e0ef81989ae78cfb19ef
Reviewed-by: Christian Stromme <christian.stromme@digia.com>