avformat/mov: Do not zero memory that is written too or unused

Fixes: OOM
Fixes: 31220/clusterfuzz-testcase-minimized-ffmpeg_dem_MOV_fuzzer-6033383962574848

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 c1fe1114bc)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/mov.c

@@ -3022,7 +3022,7 @@ static int mov_read_sdtp(MOVContext *c, AVIOContext *pb, MOVAtom atom)
     av_freep(&sc->sdtp_data);
     sc->sdtp_count = 0;
 
-    sc->sdtp_data = av_mallocz(entries);
+    sc->sdtp_data = av_malloc(entries);
     if (!sc->sdtp_data)
         return AVERROR(ENOMEM);