Distributed sort on a large data set may result in incorrect results.

This is a recently added bug. This bug causes incorrect order results when the number of partition ranges are more than one. This patch fixes the bug.

This is an urgent bug fix. The unit test to reproduce this case requires session variables to change the default TajoConf settings. In other words, for it, we need the resolution of TAJO-928. After TAJO-928, I'll add an unit test in another Jira (TAJO-970).