fix: _sql_query eviction query logic

Summary

• fix: _sql_query eviction query logic

There was a bug when SQL statistics LRU removed some old query from the _sql_query table. The query ref_counter field in unsigned, but the code decremented it below zero in the space on eviction. That produced an error (fixed).

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• Close #928 (closed)
• Cherry-pick to: none
• Docs follow-up: not necessary