dlna_dmr: Allow for upnp attributes with None contents

[chishm]

Proposed change

When getting device manufacturer or modelName from SSDP discovery info, treat all falsey values as an empty string. This is a minor bug fix for an edge case in some weird DLNA-DMR devices.

This bug fix can be safely cherry-picked to the current release.

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 Source: components/dlna_dmr/config_flow.py:477 AttributeError: 'NoneType' object has no attribute 'lower' #63575
• This PR is related to issue:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
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• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

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• The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
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  Updated by running python3 -m script.gen_requirements_all.
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[probot-home-assistant]

Hey there @StevenLooman, mind taking a look at this pull request as it has been labeled with an integration (dlna_dmr) you are listed as a code owner for? Thanks!
_{^{(message by CodeOwnersMention)}}

[frenck]

Thanks, @chishm 👍