If we did a mode set, the gamma may have been changed by the kernel, and
if we didn't also update the gamma in the same transaction, we have no
way to predict the current gamma ramp state. In this case, read the
gamma state directly from KMS.
This should be relatively harmless regarding the race conditions the
state prediction was meant to solve, as the worst case is we get none or
out of date gamma ramps; and since this is for when gamma ramps are not
updated at mode setting time, we'd get intermediate gamma state to begin
with, so it's not worse than what we currently do anyway.
Fixes: https://gitlab.gnome.org/GNOME/mutter/issues/851https://gitlab.gnome.org/GNOME/mutter/merge_requests/840
1b4709794e