Fix -Wrange-loop-analysis warnings

Summary: These warnings were introduced in D4221.

Test Plan:
With Clang as a compiler:

ninja check

Ensure there is no -Wrange-loop-analysis during the build.

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D4283