Ensure all statements are dropped before closing sqlite connection

[hasali19]

Fixes #272

[mehcode]

Thanks for the fix. Error looks like a spurious ui test failure.

cc @abonander

[sgg]

FYI when I was working on the realworld example I was running into an issue where tables would end up locked if a transaction exited prematurely (e.g. due to a query failing).

This change seems to have fixed that issue!