Fix table column getColumnIndex undefined bug

[406087475]

Fix table column getColumnIndex undefined bug

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[pull-request-triage]

👋 @406087475, seems like this is your first time contribution to element-plus.

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[github-actions]

[github-actions]

Hello @406087475, thank you for contributing to element-plus, please see our guideline to see how to make contribution

[btea]

Thank you for your contribution, but it is duplicated with #16781.

[Liao-js]

Can you provide a use case scenario where the error occurs?

[Liao-js]

I will close my PR