avformat/mov: Check for duplicate st3d

Fixes: memleak
Fixes: 29585/clusterfuzz-testcase-minimized-ffmpeg_dem_MOV_fuzzer-6594188688490496

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 658f0606cb)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/mov.c

@@ -5518,6 +5518,10 @@ static int mov_read_st3d(MOVContext *c, AVIOContext *pb, MOVAtom atom)
         av_log(c->fc, AV_LOG_ERROR, "Empty stereoscopic video box\n");
         return AVERROR_INVALIDDATA;
     }
+
+    if (sc->stereo3d)
+        return AVERROR_INVALIDDATA;
+
     avio_skip(pb, 4); /* version + flags */
 
     mode = avio_r8(pb);