Editc: Index error message should have priority over missing fields

[nus-pe-bot]

Steps to Reproduce:

1. Open App
2. Enter "editc 14" when there is less than 14 contact entries

Expected Behavior: The error message for the invalidness of the index should be prioritized over missing fields.

Actual Behavior: "At least one field to edit must be provided." I understand that this may be a bit contentious, but intuitively it feels like that an obviously wrong index should have priority over other missing fields for this tester.

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_{[original: nus-cs2103-AY2021S1/pe-interim#6023]}

[jazerler]

Team's Response

An edit command with a valid index and no fields cannot ever be accepted as a valid command, but an edit command with invalid index and valid fields can be accepted until it attempts to find if the index is valid.

Duplicate status (if any):

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