Fix transactions for non-autocommitting handles

[hgschmie]

If a handle is by default using autocommit == false, then transactions
could be commited (or rolled back) without having to call
Handle#begin() first. This broke in 3.41.1.

Restore the old behavior. Fixes #2491

[sonarcloud]

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[stevenschlansker]

Is this expected to work? It seems a little weird to hand off an in-flight transaction to Jdbi. But I suppose breaking user code sucks too

[hgschmie]

well, not sure how to answer that. But up until 3.41.1, you could turn autocommit off on a connection, pile a bunch of statements onto it and then call Handle#commit(). You probably shouldn't but it still worked.

What the change does is basically looking at the commit state of the connection when the transaction handler is created and if it has autocommit already turned off, it moves the state machine "one state further". So the handler is in the same state if you opened it with a connection that has auto-commit turned off as with a regular (autocommit on) + Handle#begin().

I still think it is a cornercase that the user stumbled upon and if it hadn't worked in the past, I would not make that change. I also think it is benign for "regular" use one can call begin multiple times.