FIX: Allow a user to remove their title

Somewhere there was a regression and a user couldn't remove their own
title. If they selected '(none)' in the UI it would say it was saved,
but it would not actually be updated in the db.

lib/guardian.rb

@@ -222,6 +222,7 @@ class Guardian
   def can_grant_title?(user, title = nil)
     return true if user && is_staff?
     return false if title.nil?
+    return true if title.empty? # A title set to '(none)' in the UI is an empty string
     return false if user != @user
     return true if user.badges.where(name: title, allow_title: true).exists?
     user.groups.where(title: title).exists?

spec/components/guardian_spec.rb

@@ -2243,6 +2243,10 @@ describe Guardian do
       it "returns false if title is from a group the user doesn't belong to" do
         expect(Guardian.new(user).can_grant_title?(user, group.title)).to eq(false)
       end
+
+      it "returns true if the title is set to an empty string" do
+        expect(Guardian.new(user).can_grant_title?(user, '')).to eq(true)
+      end
     end
   end