SEO fields setting should not be shown on node type add form

Problem/Motivation

The SEO fields setting on node type forms is useless if the type does not yet exist.
This will also cause problems if hooks ever get type checked / replaced by events with type checking as evidenced when using hook_event_dispatcher (typechecks on hook_entity_bundle_field_info_alter).

Proposed resolution

Add a check to see if the bundle exists before adding the SEO setting fields.