test: add tests for bad-txns-prevout-null reject reason

Summary:

Basically this condition is met for non-coinbase transactions with coinbase-like outpoints, i.e. hash=0, n=0xffffffff.

Backport of core#22408.

Test Plan:

ninja check-functional-extended

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D12217