Fix possible double-free in Aggregator

[nickitat]

Changelog category (leave one):

• Bug Fix (user-visible misbehavior in an official stable release)

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

Fixed very unlikely double-free attempt on aggregation state memory in case of memory limit exception.

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Problem was in convertToBlockImplNotFinal. To avoid double-free we set mapped = nullptr after inserting into aggr function column. We rely on reserve here to avoid exception between insertion into first aggr function column and mapped = nullptr (l. 2148). When return_single_block is true we preallocated not enough memory, so exception was still possible.

ASan report

[robot-clickhouse-ci-1]

This is an automated comment for commit cd193ed with description of existing statuses. It's updated for the latest CI running
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[nickitat]

only Bugfix validate check is red