Fix MergeJoinScan next logic

[tishyakhanna97]

Changes in this PR

• [X] Bug fix
• [ ] New feature
• [ ] Breaking change of an existing feature
• [ ] Refactor/Performance enhancements

Overview

We were skipping the "next" call in the LHS table, causing the pointer on the LHS table to remain there permanently. This caused an infinite loop, which can be seen here https://github.com/don-tay/simpledb/issues/23