let user set codec even if CODEC_ID_NONE is default patch by (Luca Abeni: lucabe72, email it)

Originally committed as revision 4466 to svn://svn.ffmpeg.org/ffmpeg/trunk

ffmpeg.c

@@ -3607,8 +3607,8 @@ static void opt_output_file(const char *filename)
             exit(1);
         }
     } else {
-        use_video = file_oformat->video_codec != CODEC_ID_NONE || video_stream_copy;
-        use_audio = file_oformat->audio_codec != CODEC_ID_NONE || audio_stream_copy;
+        use_video = file_oformat->video_codec != CODEC_ID_NONE || video_stream_copy || video_codec_id != CODEC_ID_NONE;
+        use_audio = file_oformat->audio_codec != CODEC_ID_NONE || audio_stream_copy || audio_codec_id != CODEC_ID_NONE;
 
         /* disable if no corresponding type found and at least one
            input file */