command_line: Do not lead to erroring out code indexing None or empty discovery_info

[yarikoptic]

Proposed change

Just make code more "correct" as signature allows for None but then code assumes that it is a DiscoveryInfoType. In this case also in case of an empty constract or none - just return with a warning (since I guess it is unexpected)

Type of change

• [ ] Dependency upgrade

• [x] Bugfix (non-breaking change which fixes an issue)

• [ ] New integration (thank you!)

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• [ ] Code quality improvements to existing code or addition of tests

• This PR fixes or closes issue: fixes #116871

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[home-assistant[bot]]

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

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