br: Fix RangeTree.GetIncompleteRange when the rangeTree is empty. (#37086)

[ti-chi-bot]

This is an automated cherry-pick of #37086

Issue Number: #37085

Signed-off-by: pingyu yuping@pingcap.com

What problem does this PR solve?

Issue Number: close #37085

Problem Summary: RangeTree.GetIncompleteRange return wrong result when the rangeTree is empty

What is changed and how it works?

1. Judge whether rangeTree is empty (by pivot can be found or not).
2. Return the last range if pivot is not found.
3. Also revert the work around to this issue introduced in #32614 for raw backup.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

Fix `RangeTree.GetIncompleteRange` when the `rangeTree` is empty.

[BornChanger]

/retest

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: BornChanger, Leavrth

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• OWNERS [Leavrth]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-08-17 03:10:08.661573545 +0000 UTC m=+773373.210589529: ☑️ agreed by Leavrth.
• 2023-08-17 04:10:00.150186504 +0000 UTC m=+776964.699202490: ☑️ agreed by BornChanger.

[BornChanger]

/retest

[codecov]

Codecov Report

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Additional details and impacted files

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