Minor, subtle bug in error handling in covert_fields_widget()

In the function covert_fields_widget(), error handling code ensures that the Covert Fields module is only handling a widget it recognizes. Unfortunately, if the error handling code is ever actually invoked, the error message will be "covert_fields does not know how to handle widget type """, which isn't very helpful. The cause is that $widget['type'] should be $field['widget']['type'].

The attached patch corrects this subtle bug. The good news is that the erroneous code would almost certainly have never been invoked, but the bug does show up if you're creating a new module based off of Covert Fields and a widget is named improperly.