Fix opensense map when data during startup

[cgtobi]

Description:

Raise not ready when no data from API is retrieved. This could happen when there is too much IO during startup and the query times out.

Related issue (if applicable): fixes #

Pull request with documentation for home-assistant.io (if applicable): home-assistant/home-assistant.io#<home-assistant.io PR number goes here>

Example entry for configuration.yaml (if applicable):

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. 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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• Documentation added/updated in home-assistant.io

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If the code does not interact with devices:

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