bitrate sanity check (fixes assertion failure)

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@8293 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavcodec/wmaenc.c

@@ -36,6 +36,9 @@ static int encode_init(AVCodecContext * avctx){
     if(avctx->channels > MAX_CHANNELS)
         return -1;
 
+    if(avctx->bit_rate < 24*1000)
+        return -1;
+
     /* extract flag infos */
     flags1 = 0;
     flags2 = 1;