Improve invalid vout value rpc error message

Summary:
Since the vout value can start at 0, the error message for negative values can be improved to something like: vout cannot be negative.

This is a backport of core#19956

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D10423