fixes #42042 (#42939)

Do not create group with empty name when region (optional argument) is 
not given in the openstack connection

changelogs/fragments/42042-inventory_with_no_region.yaml

@@ -0,0 +1,2 @@
+bugfixes:
+- plugins/inventory/openstack.py - Do not create group with empty name if region is not set

lib/ansible/plugins/inventory/openstack.py

@@ -258,7 +258,8 @@ class InventoryModule(BaseInventoryPlugin, Constructable, Cacheable):
         groups.append(cloud)
 
         # Create a group on region
-        groups.append(region)
+        if region:
+            groups.append(region)
 
         # And one by cloud_region
         groups.append("%s_%s" % (cloud, region))