Item Cost can be negative when adding a new item

[lestersimjj]

Describe the bug
When adding an item, a user can enter a negative cost and no errors were raised.

To Reproduce

add n/`testspeakers` s/`12345` t/`Speaker` c/`-100` pf/`Loud_Technologies` pd/`2022-02-23`

Expected Behavior
Error. Please ensure that the item cost is larger than $0.

Actual Behavior
Equipment successfully added: testspeakers, serial number 12345

Screenshots

[nus-se-bot]

Team's Response

Duplicate of #512. Severity adjusted to Low as it does not affect usage of application.

The 'Original' Bug

[The team marked this bug as a duplicate of the following bug]

Negative cost should not be allowed

I think that negative cost for the products should not be allowed by default, unless there is a reason for it, in which case it would be good to document it.

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_{[original: nus-cs2113-AY2122S2/pe-interim#601] [original labels: type.FeatureFlaw severity.Medium]}

Their Response to the 'Original' Bug

[This is the team's response to the above 'original' bug]

Does not affect operation of the application so severity should be low.

Items for the Tester to Verify

:question: Issue duplicate status

Team chose to mark this issue as a duplicate of another issue (as explained in the Team's response above)

• [ ] I disagree

Reason for disagreement: [replace this with your explanation]

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:question: Issue type

Team chose [type.FeatureFlaw] Originally [type.FunctionalityBug]

• [ ] I disagree

Reason for disagreement: [replace this with your explanation]

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:question: Issue severity

Team chose [severity.Low] Originally [severity.Medium]

• [ ] I disagree

Reason for disagreement: [replace this with your explanation]

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