fix conn upgrade lock

[MarinPostma]

There was a deadlock when a conn failed to upgrade to a write lock, because there's nothing to rollback. This happens in scenarios such as:

C1: BEGIN
C1: SELECT * FROM test
C2: INSERT INTO TEST
C1: INSERT INTO TEST

C1 fails to upgrade it's lock, but it has a shallow lock in the connection manager. Aborting the transaction would have no effect because it doesn't own a sqlite lock.