Fixed a PHP warning in DBALException::driverExceptionDuringQuery()

When a query parameter contains binary data, `driverExceptionDuringQuery()` generates a PHP warning. This is because it internally uses `json_encode()`, which expects valid UTF-8 strings (at least in PHP 5.4.13).

This PR removes the warning with the `@` operator. `json_encode()` will still return a string representation, replacing the binary data with `null`.

I added a test that fails before the fix.