avformat/mov: Use int64_t in intermediate for corrected_dts

Fixes: CID1500312 Unintentional integer overflow

Sponsored-by: Sovereign Tech Fund
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 034054b370)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/mov.c

@@ -3209,7 +3209,7 @@ static int mov_read_stts(MOVContext *c, AVIOContext *pb, MOVAtom atom)
             sc->stts_data[i].duration = 1;
             corrected_dts += (delta_magnitude < 0 ? (int64_t)delta_magnitude : 1) * sample_count;
         } else {
-            corrected_dts += sample_duration * sample_count;
+            corrected_dts += sample_duration * (int64_t)sample_count;
         }
 
         current_dts += sc->stts_data[i].duration * (int64_t)sample_count;