segfault fix

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@4295 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavformat/mov.c

@@ -772,11 +772,13 @@ static int mov_read_stco(MOVContext *c, ByteIOContext *pb, MOV_atom_t atom)
     
     for(i=0; i<c->fc->nb_streams; i++){
         MOVStreamContext *sc2 = (MOVStreamContext *)c->fc->streams[i]->priv_data;
+        if(sc2 && sc2->chunk_offsets){
             int64_t first= sc2->chunk_offsets[0];
             int64_t last= sc2->chunk_offsets[sc2->chunk_count-1];
             if(first >= sc->chunk_offsets[entries-1] || last <= sc->chunk_offsets[0])
                 c->ni=1;
         }
+    }
 #ifdef DEBUG
 /*
     for(i=0; i<entries; i++) {