views: improve HTTP 400 errors

> minor: To be safe. In general, we should try to keep this kind of "safety checks". They might have resulted from past bugs and/or a general approach for this module of playing it safe/pessimistic since we're interacting with a remote system that might not always match our state (I see the old function didn't have this check, but let's add it in any case).

> What we should do to improve the fuzzy points, is "enhance" the `400`s we throw around with proper error messages, so that we can better understand why things fail when users contact us.

_Originally posted by @slint in https://github.com/inveniosoftware/invenio-github/pull/109#discussion_r1257892282_