Rigify: Fix feature set not registering

When we enable the Rigify add-on with installed feature sets, we were
trying to register those feature sets as well, but failing because the
feature set list wasn't populated yet; It would ALWAYS be an empty list.

Moving refresh() inside get_enabled_modules_names() might be better.

rigify/__init__.py

@@ -166,6 +166,7 @@ class RigifyPreferences(AddonPreferences):
 
     def register_feature_sets(self, register):
         """Call register or unregister of external feature sets"""
+        self.refresh_installed_feature_sets()
         for set_name in feature_set_list.get_enabled_modules_names():
             feature_set_list.call_register_function(set_name, register)