Possible fix for #8734 (#8735)

* Possible fix for #8734

* Use explicit pool

* Use HalfStaticArray as demanded

* Use begin() instead of getBuffer()

* Combine conditions as requested

Author: aafemt

src/dsql/DsqlRequests.cpp

@@ -595,15 +595,20 @@ void DsqlDmlRequest::doExecute(thread_db* tdbb, jrd_tra** traHandle,
 			JRD_receive(tdbb, request, message->msg_number, outMsgLength, outMsg);
 
 			// if this is a singleton select that return some data, make sure there's in fact one record
-
-			if (singleton && (request->req_flags & req_active) && outMsgLength > 0)
+			if (singleton && outMsgLength > 0)
 			{
+				// No record returned though expected
+				if (!(request->req_flags & req_active))
+				{
+					status_exception::raise(Arg::Gds(isc_stream_eof));
+				}
+
 				// Create a temp message buffer and try one more receive.
 				// If it succeed then the next record exists.
 
-				std::unique_ptr<UCHAR[]> message_buffer(new UCHAR[outMsgLength]);
+				HalfStaticArray<UCHAR, BUFFER_SMALL> message_buffer(getPool(), outMsgLength);
 
-				JRD_receive(tdbb, request, message->msg_number, outMsgLength, message_buffer.get());
+				JRD_receive(tdbb, request, message->msg_number, outMsgLength, message_buffer.begin());
 
 				// Still active request means that second record exists
 				if ((request->req_flags & req_active))