AVERROR_NOFMT if the format is unknown / cannot be recognized.

It is returned AVERROR_INVALIDDATA, in the sense that the data is
invalid within what the specific libav* binary supports.

That was the last remaining use of AVERROR_NOFMT, which is going to be
dropped at the next libavutil major bump.

Originally committed as revision 22625 to svn://svn.ffmpeg.org/ffmpeg/trunk