Fix UniFi remove client service if time stamps are not integers

[Kane610]

Breaking change

Proposed change

Verify that both first and last seen are not None, else client can be removed

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes Failure to run unifi.remove_clients service call #63728
• This PR is related to issue:
• Link to documentation pull request:

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[Kane610]

Awesome! Thanks @thecode 🎉