openvswitch_bridge.py: Avoid runtime error with no external_ids (#25128)

This happens when there is external_ids configured on the existing
OvS bridge, though playbook doesn't.

lib/ansible/modules/network/ovs/openvswitch_bridge.py

@@ -157,11 +157,12 @@ def map_obj_to_commands(want, have, module):
                 templatized_command = ("%(ovs-vsctl)s -t %(timeout)s"
                                        " br-set-external-id %(bridge)s")
                 command = templatized_command % module.params
-                for k, v in iteritems(want['external_ids']):
-                    if (k not in have['external_ids']
-                            or want['external_ids'][k] != have['external_ids'][k]):
-                        command += " " + k + " " + v
-                        commands.append(command)
+                if want['external_ids']:
+                    for k, v in iteritems(want['external_ids']):
+                        if (k not in have['external_ids']
+                                or want['external_ids'][k] != have['external_ids'][k]):
+                            command += " " + k + " " + v
+                            commands.append(command)
         else:
             templatized_command = ("%(ovs-vsctl)s -t %(timeout)s add-br"
                                    " %(bridge)s")