mov: reject zero bytes_per_frame with non-zero samples_per_frame

In this case the mov demuxer can return a large number of empty packets.

Reviewed-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>

libavformat/mov.c

@@ -2587,6 +2587,13 @@ static void mov_build_index(MOVContext *mov, AVStream *st)
                 AVIndexEntry *e;
                 unsigned size, samples;
 
+                if (sc->samples_per_frame > 1 && !sc->bytes_per_frame) {
+                    avpriv_request_sample(mov->fc,
+                           "Zero bytes per frame, but %d samples per frame",
+                           sc->samples_per_frame);
+                    return;
+                }
+
                 if (sc->samples_per_frame >= 160) { // gsm
                     samples = sc->samples_per_frame;
                     size = sc->bytes_per_frame;