Avoid failing when hub does not provide cover position information

[Franchie]

The powerview hub, seemingly randomly, will occasionally not
provide data for cover positions. Some requests will return the
desired response, but minutes later the same request might not.

It appears this issue is being experienced by a number of people:
https://community.home-assistant.io/t/hunter-douglas-powerview-component-expanding-this-api/88635/48

While an unfortunate bug with the hub, crashing the integration
as a result of this missing data appears somewhat excessive.
This patch adds a simple check to ensure the 'position' key
has been returned by the hub before attempting to access its
data.

Proposed change

This does a conditional check for existence of the "positions" key within the returned raw data from the hub.
If that does not exist, an empty dictionary is returned instead then later checks avoid accessing the unavailable data.

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 #
• 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
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• Tests have been added to verify that the new code works.

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[homeassistant]

Hi @Franchie,

It seems you haven't yet signed a CLA. Please do so here.

Once you do that we will be able to review and accept this pull request.

Thanks!

[probot-home-assistant]

Hey there @bdraco, mind taking a look at this pull request as its been labeled with an integration (hunterdouglas_powerview) you are listed as a codeowner for? Thanks!
_{^{(message by CodeOwnersMention)}}

[bdraco]

I've never had mine do that, but these talk over RF so its not really surprising. It may be an hub v1 issue per #36040

[bdraco]

Still works as expected ( I wouldn't expect otherwise with this small of a change )

[Franchie]

Yes, it is a v1 hub, and I know from use that the RF to this particular blind is troublesome. That's likely what's causing the random drops.
Thanks for your work on this integration, it's awesome!