I have updated the diff according to Aaron's suggestions.

Hello,

right now when "Enable signing plasmoid" is enabled if the user doesn't choose a gpg key,
plasmate won't have a key enabled. So "Enable signing plasmoid", will be enabled but no signing will
happen. 

How to test the issue,
- rm ${KDEHOME}/share/config/plasmaterc
-create a gpg key(gpg --gen-key)
-open plasmate
-click publisher
-click enable

It works.