v.18.12Bug Fix

Fixed Block Structure Mismatch Error in UNION Stream for Distributed Queries

Fixed the Block structure mismatch in UNION stream: different number of columns error that occurred for distributed queries if one of the shards is local and the other is not, and optimization of the move to PREWHERE is triggered. #2226 #3037 #3055 #3065 #3073 #3090 #3093