Make write_streamheader() return a meaningful error code if no codec

tag is defined, rather than return -1.

Originally committed as revision 23433 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/nutenc.c

@@ -405,7 +405,7 @@ static int write_streamheader(AVFormatContext *avctx, ByteIOContext *bc, AVStrea
     if (codec->codec_tag){
         put_le32(bc, codec->codec_tag);
     }else
-        return -1;
+        return AVERROR(EINVAL);
 
     put_v(bc, nut->stream[i].time_base - nut->time_base);
     put_v(bc, nut->stream[i].msb_pts_shift);