Fix firewalld module failing on missing protocol. (ansible#50242)

Under Python 3.7 at least, the split of the port field fails
ungracefully if there is no slash. The fix also addresses the
case of an empty protocol after the slash.

lib/ansible/modules/system/firewalld.py

@@ -679,8 +679,11 @@ def main():
     zone = module.params['zone']
 
     if module.params['port'] is not None:
-        port, protocol = module.params['port'].strip().split('/')
-        if protocol is None:
+        if '/' in module.params['port']:
+            port, protocol = module.params['port'].strip().split('/')
+        else:
+            protocol = None
+        if not protocol:
             module.fail_json(msg='improper port format (missing protocol?)')
     else:
         port = None