[fix](block) fix be core while mutable block merge may cause different row size between columns in origin block (#27943)

be/src/exec/exec_node.cpp

@@ -561,6 +561,7 @@ Status ExecNode::do_projections(vectorized::Block* origin_block, vectorized::Blo
             }
         }
         DCHECK(mutable_block.rows() == rows);
+        output_block->set_columns(std::move(mutable_columns));
     }
 
     return Status::OK();