ac3probe: Detect Sonic Foundry Soft Encode AC3 as raw AC3.

Our ac3 code chain can handle it fine.
More ideal would be to write a demuxer that actually extracts what can be from the additional
headers and uses it for whatever it can be used for.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 30ca700ba17b9ba46f4648afa30559ad890f0221)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/ac3dec.c

@@ -40,6 +40,8 @@ static int ac3_eac3_probe(AVProbeData *p, enum CodecID expected_codec_id)
         buf2 = buf;
 
         for(frames = 0; buf2 < end; frames++) {
+            if(!memcmp(buf2, "\x1\x10\0\0\0\0\0\0", 8))
+                buf2+=16;
             init_get_bits(&gbc, buf2, 54);
             if(ff_ac3_parse_header(&gbc, &hdr) < 0)
                 break;