improve switch

Author: uzhastik

ydb/core/kqp/executer_actor/kqp_executer_impl.h

@@ -1140,6 +1140,7 @@ class TKqpExecuterBase : public TActorBootstrapped<TDerived> {
 
                 case NKqpProto::TKqpPhyConnection::kStreamLookup:
                     UnknownAffectedShardCount = true;
+		    [[fallthrough]];
                 case NKqpProto::TKqpPhyConnection::kMap:
                     partitionsCount = originStageInfo.Tasks.size();
                     break;