mov: skip version and flags attributes in mov_read_chan()

Fixes decting channel layout for files with uncommon audio, such as
FL and FR in two separate streams. Introduced in 3bab7cd.

CC: libav-devel@libav.org
Sample-Id: ticket1474.mov
Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>

libavformat/mov.c

@@ -634,6 +634,9 @@ static int mov_read_chan(MOVContext *c, AVIOContext *pb, MOVAtom atom)
     if (atom.size < 16)
         return 0;
 
+    /* skip version and flags */
+    avio_skip(pb, 4);
+
     ff_mov_read_chan(c->fc, pb, st, atom.size - 4);
 
     return 0;