Panelizer attempts to save empty configurations

I was receiving strict warning errors and applied the patch in https://www.drupal.org/node/1988250, which almost solved my problem. However, in cases where we have no view modes panelized (save for Full Page Override), I would get a few errors like "Warning: Creating default object from empty value in PanelizerEntityDefault->hook_entity_update()" ultimately resulting in a PDOException:

PDOException: SQLSTATE[HY000]: General error: 1364 Field 'did' doesn't have a default value: INSERT INTO {panelizer_entity} (entity_type, entity_id, revision_id, view_mode) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3)

I attached a patch that addresses this by skipping empty $panelizer variables in hook_entity_update().

I've rolled the attached patch against 7.x-3.1 (the version I'm using), but the issue appears to persist in the dev branch as well. I'm happy to re-roll against 7.x-3.x if you'd like.