SQLite3: Have to finalize statements before closing database handle

[DL6ER]

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Imagine the following situation: A user queries some extensive data on the log term dashboard. This will cause the database to be locked for maybe up to 30 seconds. If FTL wants to write in this time window to the database, it is actually allowed to open and use it as PHP is explicitly requesting only read-only access to the database. We can even prepare all queries we want to add to the database in a TRANSACTION, however, at the end of the transaction, we won't be able to save them as the database is locked against any writes.

Problem: Since the statement that was supposed to write queries to the database is not yet finalized, sqlite3_close() actually fails and FTL keeps the database handle open forever (in an undefined status) as we haven't even considered that close can fail due to locked (I though closing will be just fine and unlock, but that is not guaranteed to be the case!).

Solution: We finalize all statements before calling sqlite3_close() after an error, that may or not be caused by a database lock. In addition, we now also check the return value of sqlite3_close() and print some error message in the future if closing the database failed (although we don't expect this to happen anymore).

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