Fix double iteration bug when resumed from a checkpoint.

[sudiptob2]

What does this PR do?

This PR fixes the double iter() bug discussed in #19427

Fixes #19427

Before submitting

• Was this discussed/agreed via a GitHub issue? (not for typos and docs)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure your PR does only one thing, instead of bundling different changes together?
• Did you make sure to update the documentation with your changes? (if necessary)
• Did you write any new necessary tests? (not for typos and docs)
• Did you verify new and existing tests pass locally with your changes?
• Did you list all the breaking changes introduced by this pull request?
• Did you update the CHANGELOG? (not for typos, docs, test updates, or minor internal changes/refactors)

PR review

Anyone in the community is welcome to review the PR.
Before you start reviewing, make sure you have read the review guidelines. In short, see the following bullet-list:

Reviewer checklist

• Is this pull request ready for review? (if not, please submit in draft mode)
• Check that all items from Before submitting are resolved
• Make sure the title is self-explanatory and the description concisely explains the PR
• Add labels and milestones (and optionally projects) to the PR so it can be classified

---

📚 Documentation preview 📚: https://pytorch-lightning--20775.org.readthedocs.build/en/20775/

[sudiptob2]

@Borda Thanks for the review! Let me know if there's anything you'd like me to change. Otherwise, can we go ahead and merge this?

[Borda]

Suggested change

	# Only call iter() if:
	# 1. Not restarting AND
	# 2. Not resuming from checkpoint (not _is_resuming) AND
	# 3. Past first epoch (current_epoch > 0)
	# Only call `iter()` if all following cases:
	# 1. Not restarting
	# 2. Not resuming from checkpoint (not _is_resuming)
	# 3. Past first epoch (current_epoch > 0)

[sudiptob2]

Hey, @Borda just wondering if anything is blocking this PR from merging?