Upgrade from standard to hotfix release fails on 1.12.0

Describe the bug

Upgrade from non-hotifx to a hotfix release fails when pan-os-python==1.12.0

Reverting to pan-os-python 1.11.0 works just fine.

Expected behavior

Device is upgraded

Current behavior

Traceback (most recent call last):
  File ".../venv/lib/python3.11/site-packages/nornir/core/task.py", line 99, in start
    r = self.task(self, **self.params)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../panos_upgrade/run.py", line 197, in upgrade_device
    upgrade_successful = fw.software.upgrade_to_version(target_version)
                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../venv/lib/python3.11/site-packages/panos/updater.py", line 337, in upgrade_to_version
    elif not self._direct_upgrade_possible(
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../venv/lib/python3.11/site-packages/panos/updater.py", line 519, in _direct_upgrade_possible
    and current_version.subrelease_num < target_version.subrelease_num
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: '<' not supported between instances of 'NoneType' and 'int'

Possible solution

Seems the issue is that there is no value for subrelease_num if not coming from a hotfix release. Either populate that with 0, or account for it in the conditional.

Some quick and dirty testing:

>>> from panos import PanOSVersion
>>> t = PanOSVersion("10.1.13-h1")
>>> c = PanOSVersion('10.1.13')
>>> t
PanOSVersion ('10.1.13-h1')
>>> c
PanOSVersion ('10.1.13')
>>> c.subrelease_num
>>> t.subrelease_num
1
>>>

Steps to reproduce

Try to upgrade a firewall from 10.1.13 to 10.1.13-h1 using upgrade_to_version()

Screenshots

n/a

Context

Cannot use this to apply hotfix releases if coming from a normal release.

Your Environment

• Version used: 1.12.0
• Environment name and version (e.g. Chrome 59, node.js 5.4, python 3.7.3): python 3.11.9
• Operating System and version (desktop or mobile): MacOS

Start in panos/updater.py at upgrade_to_version() and _direct_upgrade_possible(), then inspect how PanOSVersion parses normal and hotfix versions. Reproduce the 10.1.13 to 10.1.13-h1 upgrade using upgrade_to_version(); done means the comparison no longer raises TypeError and the device upgrade proceeds as expected.