avformat/mov: check that pcmC box is of the expected type

As per 23003-5:2020 this box is defined as
PCMConfig extends FullBox(‘pcmC’, version = 0, 0), which means
that version is 0 and flags should be zero.

libavformat/mov.c

@@ -1590,14 +1590,23 @@ static int mov_read_enda(MOVContext *c, AVIOContext *pb, MOVAtom atom)
 static int mov_read_pcmc(MOVContext *c, AVIOContext *pb, MOVAtom atom)
 {
     int format_flags;
+    int version, flags;
 
     if (atom.size < 6) {
         av_log(c->fc, AV_LOG_ERROR, "Empty pcmC box\n");
         return AVERROR_INVALIDDATA;
     }
 
-    avio_r8(pb);    // version
-    avio_rb24(pb);  // flags
+    version = avio_r8(pb);
+    flags   = avio_rb24(pb);
+
+    if (version != 0 || flags != 0) {
+        av_log(c->fc, AV_LOG_ERROR,
+               "Unsupported 'pcmC' box with version %d, flags: %x",
+               version, flags);
+        return AVERROR_INVALIDDATA;
+    }
+
     format_flags = avio_r8(pb);
     if (format_flags == 1) // indicates little-endian format. If not present, big-endian format is used
         set_last_stream_little_endian(c->fc);