```
Previously the argument would be untouched if the first block scan
failed. This makes the behavior predictable, and consistent with the
documentation.
```
Backport of core [[https://github.com/bitcoin/bitcoin/pull/14957 | PR14957]] and the remaining of [[https://github.com/bitcoin/bitcoin/pull/15321 | PR15321]] (see D5238).
Depends on D5563.