add not saved err to role change rescues

Author: ezekg

app/models/concerns/roleable.rb

@@ -20,7 +20,8 @@ def change_role!(name)
 
     def change_role(name)
       change_role!(name)
-    rescue ActiveRecord::RecordInvalid
+    rescue ActiveRecord::RecordNotSaved,
+           ActiveRecord::RecordInvalid
       nil
     end