fix: stationBoard entries can be nullish

[121593]

Station board sometimes returns {}, causing an error to be thrown when calling entries.flat().

Should I add a test ? If yes would it go in the .har ?

[traines-source]

Thanks. Is it actually entries or one of the other fields that would have been expected for the profile you're using? Anyways, while it has the same effect, I think one could just always fall back to [].
If you have a case that reliably reproduces this, you could indeed add an integration test (see https://github.com/public-transport/db-vendo-client/blob/main/docs/tests.md#adding-integration-test-fixtures). If not, it's probably not worth the hassle and we'll just keep it as it is.

[121593]

I didn't grabbed a full dump of the call, but text content from the response is a simple {}