🐛 Backend crashes when tries to fetch proposals that drep voted on that does not exist

[MSzalowski]

Area

Wrapper

Domain

preview.gov.tools

Which wallet were you using?

No response

Context

Scenario where drep has some vote submitted into proposal, that doesn't exist in proposal table makes the govtool backend crashing.
We need to handle that.

Steps to reproduce

1. Be my DRep with malformed votes
2. Try to fetch voted proposals

Actual behavior

Backend crashes

Expected behavior

Exception should be handled properly