config dialog: Protect against null pages add.
config dialog: Protect against null pages add.

Make it resilient to null pointers pages.

pmattern/liblxqt,stefonarch/liblxqt,ThomasVie/liblxqt,stefonarch/liblxqt,lxde/liblxqt,rbazaud/liblxqt,pmattern/liblxqt,lxde/liblxqt,rbazaud/liblxqt,ThomasVie/liblxqt