Keydisabler: fix button light restore logic

Do not assign default button brightness if backup key is not found.
Instead do nothing. This will prevent brightness being reset to default
on boot when navbar is disabled.

If backup key is not found when actually toggling navbar then we've got
bigger problems.

Change-Id: I649bf1480a42f2cbe94d0a47a0c6055c934b4f56
Merge "Keydisabler: fix button light restore logic" into cm-11.0
SuperSU header
[2/2] Profile: Remove screen lock mode
[2/2] Profile: Screen timeout
[2/2] Battery light: Add 100% charged level
[2/2] Buttons: Switch to last app
[2/2] Quick pulldown: center
[2/2] Smart pulldown
[2/2] Volume panel timeout
[2/2] Global actions: Mobile data
[2/2] Global actions: Wifi
[2/2] NavBar: Enable with s-pen
[2/2] Low battery warning policy
[2/2] Recent apps: Clear all button: Location
[2/2] Recent apps: RAM bar
[2/2] Network traffic indicator
[2/2] Lockscreen notifications