Fix updating brightness while animation is still running
Review Request #125435 - Created Sept. 28, 2015 and discarded
If pressing the brightness shortcuts while the animation is still running (eg. when quickly pressing the key), it will simply ignore it. This results on my laptop (ThinkPad X220) to just react to second keypress in this case.
m_cachedBrightnessMap is updated when animation finishes. Another fix would be to update it when animation starts.
This is a followup fix for https://git.reviewboard.kde.org/r/125156/
Brightness shortcut works correctly now, even when quickly pressing the shortcut.