FIX: Destroying a user failed when it had title

...because updating the user caused a validation of the primary email and the UserEmail records are already deleted at that time.

app/models/group_user.rb

@@ -38,7 +38,7 @@ class GroupUser < ActiveRecord::Base
 
   def grant_other_available_title
     if group.title.present? && group.title == user.title
-      user.update!(title: user.next_best_title)
+      user.update_attribute(:title, user.next_best_title)
     end
   end
 

spec/models/group_spec.rb

@@ -502,6 +502,14 @@ describe Group do
       expect(user.title).to eq('Different')
       expect(user.primary_group).to eq(primary_group)
     end
+
+    it "doesn't fail when the user gets destroyed" do
+      group.update(title: 'Awesome')
+      group.add(user)
+      user.reload
+
+      UserDestroyer.new(Discourse.system_user).destroy(user)
+    end
   end
 
   it "has custom fields" do