Only validate CSV headers when CSV has headers

[miles-grant-ibigroup]

Checklist

• [ ] Appropriate branch selected (all PRs must first be merged to dev before they can be merged to master)
• [ ] Any modified or new methods or classes have helpful JSDoc and code is thoroughly commented
• [ ] The description lists all applicable issues this PR seeks to resolve
• [ ] The description lists any configuration setting(s) that differ from the default settings
• [ ] All tests and CI builds passing
• [ ] The description lists all relevant PRs included in this release (remove this if not merging to master)
• [ ] e2e tests are all passing (remove this if not merging to master)

Description

CSV Headers are not present when appending. We should not validate them as such.