Fix 'Process scheduled transactions on the last day of the month'

This commit includes a fix for MyMoneyDbTable::columnList() creating
invalid sql statement.

FIXED-IN:4.8.1
BUG:303976
Test Plan: tested on 4.8 branch
Differential Revision: https://phabricator.kde.org/D7269

(cherry picked from commit 6bce2ac0)