avformat/movenc: Don't forget to free fragment buffers

The buffers used when fragmented output is enabled have up until now not
been freed in the deinit function; they leak e.g. if one errors out of
mov_write_trailer() before one reaches the point where they are normally
written out and freed. This can e.g. happen if allocating new vos_data
fails at the beginning of mov_write_trailer().

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit e3b5316bed)

libavformat/movenc.c

@@ -6181,9 +6181,11 @@ static void mov_free(AVFormatContext *s)
             av_freep(&mov->tracks[i].vos_data);
 
         ff_mov_cenc_free(&mov->tracks[i].cenc);
+        ffio_free_dyn_buf(&mov->tracks[i].mdat_buf);
     }
 
     av_freep(&mov->tracks);
+    ffio_free_dyn_buf(&mov->mdat_buf);
 }
 
 static uint32_t rgb_to_yuv(uint32_t rgb)