[FFmpeg-devel] Add "xmv" extension to the xmv codec

[Arne Schwettmann]

I just submitted a pull request, #166, to https://github.com/FFmpeg/FFmpeg <https://github.com/FFmpeg/FFmpeg> . I am not a ffmpeg developer, but I came across this problem that the extension "xmv" is not associated with XMV format file. This quick one line change fixes that.

Thank you for considering my contribution.
Arne