Fix concatenation failure when zone is not defined

plugins/modules/service.py

@@ -96,7 +96,10 @@ def main():
 
                     break
             else:
-                module.fail_json(msg="No zone found with id " + p['zone'])
+                if p['zone'] is None:
+                    module.fail_json(msg="No zone found in domain " + p['domain'])
+                else:
+                    module.fail_json(msg="No zone found with id " + p['zone'])
                 return
             break
     else: