kcm: Guard against config being null in checkConfig()
This method is called from a queued signal and can be called when the config has been unset. Most of the other methods are already guarded against this but this one was not, causing crashes.
While I don't actually know why the config is null here, clearly it can happen as all the other methods are guarded. So make sure to do the same here.
Edited by Arjen Hiemstra