Surface error to client on OID4 issuance failure.

[wes-smith]

Right now an OID4 issuance failure results in an inscrutable 500 server error https://github.com/digitalbazaar/bedrock-vc-delivery/blob/main/lib/oid4/http.js#L211.

Probably either the issuance code that returns an empty object should instead throw, or there should be a check in this code to indicate that issuance failed.

[dlongley]

The symptom that triggers the exception here is that result doesn't have what's required to perform this destructuring:

https://github.com/digitalbazaar/bedrock-vc-delivery/blob/main/lib/oid4/http.js#L221

[dlongley]

This code:

https://github.com/digitalbazaar/bedrock-vc-delivery/blob/main/lib/issue.js#L23

Returns an empty result with nothing to destructure when there are no VCs to be issued (no VC templates, etc.). This will cause an exception and needs to be remedied.

[dlongley]

I believe the right fix here is two fold:

1. Ensure that this exception won't be thrown (some other exception can be thrown that indicates that there are no VCs issued and OID4VCI should fail with a more useful message).
2. A check that a workflow that supports OID4VCI must include at least one VC template/reference to a VC template, i.e., it must issue at least one VC. This might already be enforced for non-templated steps and, if so, we only need to do the first thing in this list, since templated steps can't be checked, I don't expect, until runtime anyway.