player: fix buggy error condition when loading mpv.conf
Install encoding-profiles.conf by default

This is probably useful.

Note that this includes a small, stupid hack to prevent loading of the
config file if vf_lavfi is not available. The profile by default uses
vf_lavfi, and the config parser will output errors if vf_lavfi is not
available.

As another caveat, we install the example profile even if encoding is
disabled (though we don't load it, since this would print errors).