player: fix --force-window on OSX

The initialization code was split and refactored for the libmpv changes.
One change, moving a part of cocoa initialization, accidentally broke
--force-window on OSX, which creates a VO in a certain initialization
stage. We still don't know how cocoa should behave with libmpv, so fix
this with a hack to beat it back into working. Untested.
vo_opengl: make :srgb decompand the BT.709 values correctly

This is the same issue as addressed by 257d9f1, except this time for
the :srgb option as well. (257d9f1 only addressed :icc-profile)

The conditions of the srgb_compand mix() call are also flipped to
prevent an off-by-one error.