avformat/mov: Fix integer overflow in mov_get_stsc_samples()

Fixes: runtime error: signed integer overflow: 5 * -2147483647 cannot be represented in type 'int'
Fixes: Chromium bug 817338
Reviewed-by: Matt Wolenetz <wolenetz@google.com>
Reported-by: Matt Wolenetz <wolenetz@google.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/mov.c

@@ -2645,7 +2645,7 @@ static inline int mov_stsc_index_valid(unsigned int index, unsigned int count)
 }
 
 /* Compute the samples value for the stsc entry at the given index. */
-static inline int mov_get_stsc_samples(MOVStreamContext *sc, unsigned int index)
+static inline int64_t mov_get_stsc_samples(MOVStreamContext *sc, unsigned int index)
 {
     int chunk_count;
 
@@ -2654,7 +2654,7 @@ static inline int mov_get_stsc_samples(MOVStreamContext *sc, unsigned int index)
     else
         chunk_count = sc->chunk_count - (sc->stsc_data[index].first - 1);
 
-    return sc->stsc_data[index].count * chunk_count;
+    return sc->stsc_data[index].count * (int64_t)chunk_count;
 }
 
 static int mov_read_stps(MOVContext *c, AVIOContext *pb, MOVAtom atom)
@@ -7189,12 +7189,13 @@ static int mov_seek_stream(AVFormatContext *s, AVStream *st, int64_t timestamp,
     /* adjust stsd index */
     time_sample = 0;
     for (i = 0; i < sc->stsc_count; i++) {
-        int next = time_sample + mov_get_stsc_samples(sc, i);
+        int64_t next = time_sample + mov_get_stsc_samples(sc, i);
         if (next > sc->current_sample) {
             sc->stsc_index = i;
             sc->stsc_sample = sc->current_sample - time_sample;
             break;
         }
+        av_assert0(next == (int)next);
         time_sample = next;
     }