Fix some memory error.

[Shylock-Hg]

What type of PR is this?

• bug
• feature
• enhancement

What does this PR do?

Fix three memory errors, and there are still other memory errors which will be traced in later.

1. Report from running tck test cases will make graph crash in Sanitizer #3503, caused by concurrent access to Session without protection.
2. In VARIABLE reduce rule, use after free
3. In match scan planner, the filter will be nullptr in some cases.

Which issue(s)/PR(s) this PR relates to?

Close #3503

Special notes for your reviewer, ex. impact of this fix, etc:

Additional context/ Design document:

Checklist:

• Documentation affected (Please add the label if documentation needs to be modified.)
• Incompatibility (If it breaks the compatibility, please describe it and add the corresponding label.）
• If it's needed to cherry-pick (If cherry-pick to some branches is required, please label the destination version(s).)
• Performance impacted: Consumes more CPU/Memory

Release notes:

Please confirm whether to be reflected in release notes and how to describe:

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[czpmango]

LGTM.

[jievince]

LGTM