internal/fuzz: release lock when reading file fails
When corpusEntryData failed in workerClient.fuzz and
workerClient.minimize, the shared memory mutex wasn't properly given up,
which would cause a deadlock when worker.cleanup was called.
This was tickled by #59062, wherein the fuzz cache directory would be
removed during operation of the fuzzer, causing corpusEntryData to fail
because the entry files no longer existed.
Updates #51484
Change-Id: Iea284041c20d1581c662bddbbc7e12191771a364
Reviewed-on: https://go-review.googlesource.com/c/go/+/476815
Run-TryBot: Roland Shoemaker <roland@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Roland Shoemaker <roland@golang.org> Reviewed-by: Bryan Mills <bcmills@google.com>