planner: quick fix the panic issue when restoring hints from a plan

[qw4990]

What problem does this PR solve?

Issue Number: ref #46791

Problem Summary: planner: quick fix the panic issue when restoring hints from a plan

What is changed and how it works?

Forget to check whether the pointer is nil before using it:

But this pointer shouldn't be nil anyway, the root cause still needs more investigation, this is just a quick fix for users.

Check List

Tests

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

  • I checked and no code files have been changed.

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.

None

[tiprow]

Hi @qw4990. Thanks for your PR.

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[elsa0520]

LGTM

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: AilinKid, elsa0520

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-11-17 10:55:39.374727247 +0000 UTC m=+4419336.961837382: ☑️ agreed by elsa0520.
• 2023-11-17 10:56:56.900561529 +0000 UTC m=+4419414.487671674: ☑️ agreed by AilinKid.