fix a panic issue in parallel agg when exception is thrown (pingcap#5433

) (pingcap#5443)

close pingcap#5356

dbms/src/DataStreams/ParallelAggregatingBlockInputStream.cpp

@@ -185,10 +185,9 @@ void ParallelAggregatingBlockInputStream::Handler::onException(std::exception_pt
     Int32 old_value = -1;
     parent.first_exception_index.compare_exchange_strong(old_value, static_cast<Int32>(thread_num), std::memory_order_seq_cst, std::memory_order_relaxed);
 
-    /// can not cancel parent inputStream or the exception might be lost
     if (!parent.executed)
         /// kill the processor so ExchangeReceiver will be closed
-        parent.processor.cancel(true);
+        parent.cancel(true);
 }