mov: Fix FPE on 0 time_scale

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/mov.c

@@ -805,6 +805,7 @@ static int mov_read_mvhd(MOVContext *c, AVIOContext *pb, MOVAtom atom)
     c->duration = (version == 1) ? avio_rb64(pb) : avio_rb32(pb); /* duration */
     // set the AVCodecContext duration because the duration of individual tracks
     // may be inaccurate
+    if (c->time_scale > 0)
         c->fc->duration = av_rescale(c->duration, AV_TIME_BASE, c->time_scale);
     avio_rb32(pb); /* preferred scale */