can't select different context when query bar is empty in normal search view

Created by: rvantonder

Issue as in title. Demo:

https://user-images.githubusercontent.com/888624/138786349-61ffd1de-a34d-4a7c-a789-a7816bc9d0a6.mp4

Labelling as bug, because (a) I'm allowed to change the context on the search home page without issue, why not here?

https://user-images.githubusercontent.com/888624/138786675-26ae1452-fe02-45c2-afe8-c0150d98ad8d.mp4

And (b) It's a valid UI state (even if it's maybe not a valid search state).

Not part of this buggy issue, but related to (b) and UX of changing context: I think I would highly prefer seeing a list of default repos when the search bar is empty and there is only context. This because context is actually part of the query, that substitutes for repo: it queries the list of repos associated with that context, so it should display that repo list by default, rather than be 'unsearchable'/empty.