Undefined var in Db::GetDataTableFromStatement

[tuan-tu-tran]

A typo breaks fetching results when statement does not have a get_result method (no myslnd) and there is no result to return, introduced by #75.

It only started breaking ever since we introduced the error handler with #88 in 4785335c290d6bbf76525b39dcf511aed89f3529

Test

• On a server where mysqlnd is not available
• Execute a db query that returns no row
• The result must be an empty array, not null