Enhancements: Suppliers "not in use" behave unexpectedly

[plocher]

I used settings to disable the suppliers I don't use / have API keys for, and ...

The "not In-Use" setting doesn't remove them from the dropdown list of suppliers used on the search page (IMO, the list should be pruned...), and

When only one supplier is still in-use, it could be auto-selected rather than leaving the field empty and forcing the user to pull down to select the only enabled supplier.

Same for Stock Location when only one location is available...