movdec: dont divide by zero when stts_data[0].duration = 0.

Fixes ticket223
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/mov.c

@@ -1527,7 +1527,7 @@ static void mov_build_index(MOVContext *mov, AVStream *st)
         int rescaled = sc->time_offset < 0 ? av_rescale(sc->time_offset, sc->time_scale, mov->time_scale) : sc->time_offset;
         current_dts = -rescaled;
         if (sc->ctts_data && sc->stts_data &&
-            sc->ctts_data[0].duration / sc->stts_data[0].duration > 16) {
+            sc->ctts_data[0].duration / FFMAX(sc->stts_data[0].duration, 1) > 16) {
             /* more than 16 frames delay, dts are likely wrong
                this happens with files created by iMovie */
             sc->wrong_dts = 1;