Delete should be more robust with an empty array of ids

... because otherwise this results in an obscure SQL syntax error.

PDOException: SQLSTATE[42000]: Syntax error or access violation: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '))' at line 1: DELETE FROM {field_collection_item} WHERE (item_id IN ()) ; Array ( ) in EntityAPIController->delete() (line 399 of /home/klausi/workspace/entity/includes/entity.controller.inc).

Patch attached.