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

@@ -157,6 +157,7 @@ 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
+                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]):