After fixing superficial issues go and work over Client's fullscreen control.
This way we:
- check first for what the rule wants uis to do,
- do only proceed if there is a change from/to fullscreen
- remove code, that becomes unneeded by this.
This goes with the assumption, that the current fullscreen state is always
correctly stored in the m_fullscreenMode variable, but the previous code
implicitly did the same at numerous occasions, just not in a consistent