firewall-cmd returns traceback when firewalld is disabled.

Reproducer:



# systemctl stop  firewalld.service

# firewall-cmd
Error: Traceback (most recent call last):
  File "/usr/lib/python3.11/site-packages/firewall/client.py", line 50, in _impl
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/site-packages/firewall/client.py", line 3145, in get_property
    return dbus_to_python(self.fw_properties.Get(
                          ^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'Get'

Proposal: Maybe no traceback when firewalld is disabled?

Reproducible: Always

Steps to Reproduce:
1. systemctl stop  firewalld.service
2. firewall-cmd
Actual Results:  
Error: Traceback (most recent call last):
  File "/usr/lib/python3.11/site-packages/firewall/client.py", line 50, in _impl
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/site-packages/firewall/client.py", line 3145, in get_property
    return dbus_to_python(self.fw_properties.Get(
                          ^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'Get'

Expected Results:  
Something beautiful and more user friendly.