Fix omission of ReadyForQuery after error with pending extended-query messages

In extended query mode, ReadyForQuery is normally deferred when there are
pending messages in the queue; it is sent only after the entire extended
query frame has been processed.

Edge case: if a message fails with an error while the queue still contains
pending messages, the queue is cleared later in the session and those
pending messages are discarded. In that case, ReadyForQuery would never be
sent.

Change: when a result indicates an error, send ReadyForQuery immediately.
The extended-query flag will still be reset later in the session. This
ensures ReadyForQuery is always emitted and prevents clients from waiting
indefinitely.

lib/PgSQL_Connection.cpp

@@ -633,8 +633,19 @@ handler_again:
 			query_result->add_error(NULL);
 		}
 
+		// Normally, ReadyForQuery is not sent immediately if we are in extended query mode
+		// and there are pending messages in the queue, as it will be sent once the entire
+		// extended query frame has been processed.
+		//
+		// Edge case: if a message fails with an error while the queue still contains pending
+		// messages, the queue will be cleared later in the session. In this situation,
+		// ReadyForQuery would never be sent because the pending messages are discarded.
+		//
+		// Fix: if the result indicates an error, explicitly send ReadyForQuery immediately.
+		// The extended query flag will still be reset later in the session.
 		if (fetch_result_end_st == ASYNC_STMT_EXECUTE_END &&
-			!myds->sess->is_extended_query_frame_empty()) {
+			!myds->sess->is_extended_query_frame_empty() &&
+			((query_result->get_result_packet_type() & PGSQL_QUERY_RESULT_ERROR) == 0)) {
 			// Skip sending ReadyForQuery if there are still extended query messages pending in the queue
 			NEXT_IMMEDIATE(fetch_result_end_st);
 		}