pidgin/pidgin

Fix a few issues with the CredentialProvider code that snuck past review

Testing Done:
Compiled and ran unit tests locally. Verified the warnings were gone from the unit test build and verified the warning was gone from the Purple-3.0.gir build.

Reviewed at https://reviews.imfreedom.org/r/168/
entry.copyable-insensitive {
color: @insensitive_fg_color;
background-color: @insensitive_bg_color;
}