Merge #10569: Fix stopatheight

Summary:
c45cbaf Fix stopatheight (Andrew Chow)

Tree-SHA512: 7df07ca1d40a5a3a8d93ad8943cd04954d587e19bbb63ed084b7aff9503788ec73a1045fbfc4a36d9775975032c2ee0bcc76eb4da10e879f483eaa6f351c19b2

Backport of Core PR 10569
https://github.com/bitcoin/bitcoin/pull/10569/files
Completes T625

Core PR 10632 was merged in Core as an answer to lack of testing for this feature, but we've already pulled it in: D953 (this doesn't mean this change was explicitly tested, but at least the behavior hasn't changed).

Test Plan:
make check
test_runner.py rpc_blockchain

Reviewers: deadalnix, Fabien, #bitcoin_abc, markblundeberg

Reviewed By: #bitcoin_abc, markblundeberg

Differential Revision: https://reviews.bitcoinabc.org/D2905