[DQ] Fix DqUnorderedOverStageInput optimizer (#9456)

Author: rvu1024

ydb/library/yql/dq/opt/dq_opt_phy.cpp

@@ -3047,15 +3047,21 @@ TMaybeNode<TExprBase> DqUnorderedOverStageInput(TExprBase node, TExprContext& ct
         return node;
     }
 
+    bool withConnections = false;
     for (size_t i = 0; i < stage.Inputs().Size(); ++i) {
         if (inputsToOptimize.Test(i)) {
             if (auto conn = stage.Inputs().Item(i).Maybe<TDqConnection>()) {
                 if (!IsSingleConsumerConnection(conn.Cast(), parentsMap, allowStageMultiUsage)) {
                     return node;
                 }
+                withConnections = true;
             }
         }
     }
+    // Stage input section may be reused multiple times
+    if (withConnections && !IsSingleConsumer(stage.Inputs(), parentsMap)) {
+        return node;
+    }
 
     TExprNode::TPtr newStageLambda;
     auto status = RemapExpr(stageLambda.Ptr(), newStageLambda, nodesToOptimize, ctx, TOptimizeExprSettings{nullptr});