async fn has_entry(cache: &DiskCache, key: &str) -> boolExpand description
Whether key has a readable entry.
Reads the value rather than asking DiskCache::has, which is an index
lookup only: an index row whose content is gone would answer true here
while every real reader still gets nothing, and a gate that reports present
for an entry nobody can read is worse than no gate.
A read error answers false: re-parsing is the safe direction.