Imports fail for entity types without custom entity class--is_new flag not set

EntityAPIController::create() sets an is_new flag, but only if the entity type has a custom 'entity class' set. Because of this, exportables support fails for entity types that don't use a custom class. The is_new flag is not set so an update rather than insert is triggered. As there's nothing to update, the code-based entity is not created.

Ran into this problem when trying to add exportable support for wysiwyg in #624018: Exportables and Features support for WYSIWYG 7.x.

Solution looks to be to pull the is_new flag setting out of the if clause in EntityAPIController::create().