group_roles_module - Avoid e-notice by early return

If there is no contact id then there is nothing further to do. However, the line which allocates a contact id gives an e-notice in this instance.  Add early return if no contact_id
Merge pull request #134 from eileenmcnaughton/patch-4

group_roles_module - Avoid e-notice by early return
Merge branch '7.x-4.4' of https://github.com/civicrm/civicrm-drupal into 7.x-4.4