fix: get credential by said 404 response

[iFergal]

rgy.reger.cloneCred or cloneCreds will cause a 500 error if the credential does not exist:

  File "/Users/fergaloconnor/dev/keri/cardano-foundation/keria/venv/lib/python3.12/site-packages/keri/vdr/viring.py", line 488, in cloneCred
    prefixer, seqner, saider = self.cancs.get(keys=(said,))
    ^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: cannot unpack non-iterable NoneType object

I fixed this in keripy to throw a missing entry error: WebOfTrust/keripy#841

So just catching that and returning 404.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.70%. Comparing base (18d3ad7) to head (5a1ad28).
Report is 19 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #282      +/-   ##
==========================================
+ Coverage   93.06%   93.70%   +0.64%     
==========================================
  Files          36       36              
  Lines        7121     7863     +742     
==========================================
+ Hits         6627     7368     +741     
- Misses        494      495       +1     

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[iFergal]

Actually, there is kering.MissingEntryError already in keripy. I think this would be better to throw from keripy - I will look at this at some point. Marking as draft.

[iFergal]

WebOfTrust/keripy#841 merged, will update this when there's a release with it and I'm free

[iFergal]

cc @2byrds

[2byrds]

LGTM