Fix issues in list feature highlighted by Hrishiraj Mandal

[apollo-tan]

Fix #188

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Files with missing lines	Coverage Δ	Complexity Δ
.../seedu/address/logic/parser/ListCommandParser.java	83.78% <100.00%> (+11.28%)	10.00 <3.00> (+1.00)