Fix exception when trying to poll a HomeKit device over Thread with no active encryption context

[Jc2k]

Proposed change

Fixes traceback when using HomeKit over Thread and polling fails when their is no active encryption context.

File "/usr/local/lib/python3.10/site-packages/aiohomekit/controller/coap/connection.py", line 158, in _decrypt_response
await self.coap_ctx.shutdown()
AttributeError: 'NoneType' object has no attribute 'shutdown'

Jc2k/aiohomekit@2.4.4...2.4.5

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
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• Breaking change (fix/feature causing existing functionality to break)
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Additional information

• This PR fixes or closes issue: fixes #
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Checklist

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[home-assistant]

Hey there @bdraco, mind taking a look at this pull request as it has been labeled with an integration (homekit_controller) you are listed as a code owner for? Thanks!

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[Jc2k]

Cheers