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.
066a418518