Check multiplexed connection before usage#1102

Enmk merged 2 commits intoantalya-25.8Altinity/ClickHouse:antalya-25.8from

bugfix/antalya-25.8/swarm_cancel_segfailtAltinity/ClickHouse:bugfix/antalya-25.8/swarm_cancel_segfailtCopy head branch name to clipboard