Fix inconsistent DPMS inhibit state.
Presentation mode toggles and inhibit requests can conflict into setting the DPMS inhibit state.
For example if presentation mode is disabled, and a request to remove inhibit is received, the DPMS inhibit state will be removed. Removing presentation mode while the screensaver is inhibited will also result in DPMS inhibit state beig removed.
To avoid such conflicts we use the same logic for DPMS inhibit as for screensaver inhibit.