* Ensure JavaScript exceptions bubble up

* Fix segfault

* Fix mutex segfault

* Fix segfault caused by memory leak

If the database was being closed, and non-exclusive work was scheduled,
it overrode the lock flag such that the state became open=false locked=false
instead of open=false locked=true. This caused queued work to not be
processed, leaking memory, which causes a segfault during napi cleanup.

Make the same changes to other methods for safe measure.