[PE-D][Tester D] Empty expenses line in spendswift.txt throws an uncaught exception

[nus-se-bot]

Steps to reproduce:

1. Add an expense
2. Exit the program
3. Remove the line heading for expense in spendswift.txt and replace it with an empty line
4. Run the program

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Labels: type.FunctionalityBug severity.Low original: wx-03/ped#6