Undo hard delete does not restore file

[nus-se-bot]

Describe the bug
A clear and concise description of what the bug is.
Undoing a hard delete does not restore the file, but restores the entry in the application

To Reproduce
Steps to reproduce the behavior:

1. Hard delete file
2. Undo
3. See error

Expected behavior
File should be restored

Screenshots
If applicable, add screenshots to help explain your problem.

Additional context
Add any other context about the problem here.

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Reported by: @nivenang
Severity: Medium

_{[original: nus-cs2103-AY1819S2/pe-dry-run#923]}