If a user saves a decoration that has a plugin but no theme we currently
delete the entry saving just the plugin/library.

This is an issue as on load we call:

const QString plugin = config.readEntry("library", s_defaultPlugin);
const QString theme = config.readEntry("theme", s_defaultTheme);

That would give us a non-default library with the default theme name,
which would be invalid.

If compiled with Breeze s_defaultTheme is blank so this ends up being
effectively the same thing. In the normal case it will neither break
nor fix anything.

None.
Just happened to see it when doing a code review.