recovered_name reduced only the head to its final path component, so a
stored name like "a.b/c" came back as "a (recovered).b/c". The whole
input is now sanitized first, and the empty-stem fallback uses the
sanitized component, which also restores idempotence for
separator-headed names ("/.dwg" used to alternate across crash cycles).
Ported from 9262d63f (#1717); its integer-precision fix landed with the
d719fb77 port, and the standalone tests/fuzz_round.rs suite (copies of
the functions rather than the code) stays out.
(cherry picked from commit 9262d63f)
Afonsop
fb674fc45e