expression: change ParamMarker.GetUserVar's func body avoid out of range

[clearcodecn]

What problem does this PR solve?

Issue Number: close #38116

Problem Summary:

call sessionVars.PreparedParams out of range 0

What is changed and how it works?

check the slice length and when slice.length > order size, then return the value,
else return default value: types.Datum

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.

None

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[ti-chi-bot]

@clearcodecn: PR needs rebase.

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