Fix leak of frame_duration_buffer in mov_fix_index().

Should be unconditionally freed at the end of mov_fix_index() in
case it hasn't been used during the fix up.

Signed-off-by: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Sasi Inguva <isasi-at-google.com@ffmpeg.org>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit d073be2291)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/mov.c

@@ -3296,6 +3296,7 @@ static void mov_fix_index(MOVContext *mov, AVStream *st)
     // Free the old index and the old CTTS structures
     av_free(e_old);
     av_free(ctts_data_old);
+    av_freep(&frame_duration_buffer);
 
     // Null terminate the index ranges array
     current_index_range++;