omadec: loosen format probing constraints

Imporoves detection of some files in the wild:

- ID3v2 a.k.a. "ea3" header is optional.
- Version and flags in ID3v2 header are unspecified.

Signed-off-by: David Goldwich <david.goldwich@gmail.com>
Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavformat/omadec.c

@@ -446,23 +446,16 @@ static int oma_read_packet(AVFormatContext *s, AVPacket *pkt)
 
 static int oma_read_probe(AVProbeData *p)
 {
-    const uint8_t *buf;
+    const uint8_t *buf = p->buf;
     unsigned tag_len = 0;
 
-    buf = p->buf;
-
-    if (p->buf_size < ID3v2_HEADER_SIZE ||
-        !ff_id3v2_match(buf, ID3v2_EA3_MAGIC) ||
-        buf[3] != 3 || // version must be 3
-        buf[4]) // flags byte zero
-        return 0;
-
-    tag_len = ff_id3v2_tag_len(buf);
+    if (p->buf_size >= ID3v2_HEADER_SIZE && ff_id3v2_match(buf, ID3v2_EA3_MAGIC))
+        tag_len = ff_id3v2_tag_len(buf);
 
     /* This check cannot overflow as tag_len has at most 28 bits */
     if (p->buf_size < tag_len + 5)
         /* EA3 header comes late, might be outside of the probe buffer */
-        return AVPROBE_SCORE_EXTENSION;
+        return tag_len ? AVPROBE_SCORE_EXTENSION : 0;
 
     buf += tag_len;