avformat/mov: Check avif_info

Fixes: leak
Fixes: 45982/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-6674082962997248
Fixes: 62164/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-6674082962997248

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/mov.c

@@ -7772,10 +7772,11 @@ static int mov_read_iloc(MOVContext *c, AVIOContext *pb, MOVAtom atom)
         return 0;
     }
 
-    if (c->fc->nb_streams) {
+    if (c->avif_info) {
         av_log(c->fc, AV_LOG_INFO, "Duplicate iloc box found\n");
         return 0;
     }
+    av_assert0(!c->fc->nb_streams);
 
     version = avio_r8(pb);
     avio_rb24(pb);  // flags.