'0' was the previous hardcoded error code. I'm just forwarding whatever SQL Error code might occur during a query.
Previous to this fix, we'd have to check for whatever Exception was thrown before DBALException in order to get the error code.
Useful when trying to come up with user-friendly error messages.
Fixing DBALException not forwarding query exception SQLSTATE codes.
The error code should be specific to the DBAL itself (assuming there is such an error code), and not to the underlying exception.