kbd backlight: Fix double brightness restore on LidOpen-resume
This fixes the issue that on LidOpen-resume the brightness might get restored two times. Once to the correct vallue and once incorrectly to 0.
To archive this it uses the same simple "don't restore to 0"-policy as is used in dimdisplay.cpp, dpms.cpp, and handlebuttonevent.cpp.
Edited by Nate Graham