libavcodec/mpegaudiodecheader.h : detect reserved mpeg id

Check the MPEG version ID for the reserved bit pattern 01, and abort the
header check in that case. This reduces the chance of misinterpreting
arbitrary data as a valid header, and prevents resulting audio artifacts.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/mpegaudiodecheader.h

@@ -62,6 +62,9 @@ static inline int ff_mpa_check_header(uint32_t header){
     /* header */
     if ((header & 0xffe00000) != 0xffe00000)
         return -1;
+    /* version check */
+    if ((header & (3<<19)) == 1)
+        return -1;
     /* layer check */
     if ((header & (3<<17)) == 0)
         return -1;