avformat/mov: fix keyframe flags for sample from chromium Issue 340865

Fixes ticket #3362.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit a0911b05)

Conflicts:
	libavformat/mov.c

libavformat/mov.c

@@ -1927,6 +1927,10 @@ static void mov_build_index(MOVContext *mov, AVStream *st)
                     if (stps_index + 1 < sc->stps_count)
                         stps_index++;
                 }
+                if (sc->keyframe_absent
+                    && !sc->stps_count
+                    && st->codec->codec_type == AVMEDIA_TYPE_AUDIO)
+                     keyframe = 1;
                 if (keyframe)
                     distance = 0;
                 sample_size = sc->alt_sample_size > 0 ? sc->alt_sample_size : sc->sample_sizes[current_sample];