Editing contact with 'edit contacts' but not also 'add contacts' is a fatal error

In 1.7, if a user has view rights to a contact, clicking the "Edit" button will cause a fatal error if the user has the permission 'edit contacts' but does not also have the 'add contacts' permission.

Cause: looking in the debugger, it appears that the Edit button is going through the contact / add bottleneck. Call to fatal() is in CRM_Core_Invoke::contact, at line 171 of CRM/Core/Invoke.php.