test: Test empty array in gettxoutproof

Summary:
This is a backport of core#19922 [3/4]
https://github.com/bitcoin/bitcoin/pull/19922/commits/faf5eb45c4a08fbfd9a8c12534bca8adfe756ef2

Depends on D10255

Test Plan: ninja check-functional

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10256