added redraw of previous frame and fixed av playback with shorter video duration
added redraw of previous frame and fixed av playback with shorter video duration

gpac/gpac,rbouqueau/gpac,RodolpheFouquet/gpac,gpac/gpac,gpac/gpac,rbouqueau/gpac,RodolpheFouquet/gpac,rbouqueau/gpac,RodolpheFouquet/gpac,gpac/gpac,rbouqueau/gpac,gpac/gpac,gpac/gpac,RodolpheFouquet/gpac,rbouqueau/gpac,rbouqueau/gpac,gpac/gpac,gpac/gpac,rbouqueau/gpac,RodolpheFouquet/gpac,RodolpheFouquet/gpac,rbouqueau/gpac