Panelizer attempts to load when it shouldn't

If Page Manager is disabled for a specific entity, e.g. node_view is disabled via "admin/structure/pages", then Panelizer should not be loaded for any pages for that entity. However, because Panelizer directly implements hook_entity_view_alter(), it will still attempt to load the configuration for the 'default' display mode.

In addition, if the entity is not enabled via Page Manager but the 'default' view mode for that entity is panelized and there are no displays configured, the pages end up not having anything displayed in the content area and a number of errors get displayed on those node pages:

• Notice: Undefined index: default in panelizer_entity_view_alter() (line 291 of panelizer.module).
• Notice: Undefined index: content in PanelizerEntityDefault->preprocess_panelizer_view_mode() (line 2595 of plugins/entity/PanelizerEntityDefault.class.php).