Correctly detect alac in mp4 properties

Should close #6570
(cherry picked from commit 7f807d9bb7cb08f1401d5cbec472338ed1d38157)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/demux/mp4/mp4.c

@@ -2028,6 +2028,11 @@ static int TrackCreateES( demux_t *p_demux, mp4_track_t *p_track,
                             p_sample->data.p_sample_soun->p_qt_description,
                             p_track->fmt.i_extra);
                 }
+                if( p_track->fmt.i_extra >= 56 && p_sample->i_type == VLC_CODEC_ALAC )
+                {
+                    p_track->fmt.audio.i_channels = *((uint8_t*)p_track->fmt.p_extra + 41);
+                    p_track->fmt.audio.i_rate = GetDWBE((uint8_t*)p_track->fmt.p_extra + 52);
+                }
                 break;
 
             /* avc1: send avcC (h264 without annexe B, ie without start code)*/