[XRandRBrightness] Don't call for xrandr if it's not available
Review Request #126146 - Created Nov. 23, 2015 and submitted
|Kai Uwe Broulik|
Check whether the extension is there before calling into it.
Also cache calls to QX11Info::connection() if we're at it.
Still works, didn't test without xrandr.
Functional patch looks fine, since the extension is not gonna mystically show up, one may wish to cache extension status validity in a tenary member (iff this constructor is called more often)
Can't tell about "unrelated changes policy" in the component ;-)