wmavoice: Check for out of bound writes

Signed-off-by: Janne Grunau <janne-libav@jannau.net>

libavcodec/wmavoice.c

@@ -1880,6 +1880,8 @@ static void copy_bits(PutBitContext *pb,
     rmn_bits = rmn_bytes = get_bits_left(gb);
     if (rmn_bits < nbits)
         return;
+    if (nbits > pb->size_in_bits - put_bits_count(pb))
+        return;
     rmn_bits &= 7; rmn_bytes >>= 3;
     if ((rmn_bits = FFMIN(rmn_bits, nbits)) > 0)
         put_bits(pb, rmn_bits, get_bits(gb, rmn_bits));