request mp3 frame_size to be set in has_codec_parameters, fix issue #1314

Originally committed as revision 20318 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/utils.c

@@ -1884,6 +1884,7 @@ static int has_codec_parameters(AVCodecContext *enc)
         if(!enc->frame_size &&
            (enc->codec_id == CODEC_ID_VORBIS ||
             enc->codec_id == CODEC_ID_AAC ||
+            enc->codec_id == CODEC_ID_MP3 ||
             enc->codec_id == CODEC_ID_SPEEX))
             return 0;
         break;