Fixed CORE-3137: Partial rollback is possible for a selectable proced…

…ure modifying data.

src/jrd/vio.cpp

@@ -2128,19 +2128,21 @@ void VIO_merge_proc_sav_points(thread_db* tdbb,
 		return;
 	}
 
-	// one by one go on putting all savepoints in the sav_point_list on
-	// top of transaction save points and call VIO_verb_cleanup()
+	// Merge all savepoints in the sav_point_list at the top
+	// of transaction save points and call VIO_verb_cleanup()
 
-	for (Savepoint* sav_point = *sav_point_list; sav_point;
-		 sav_point = sav_point->sav_next)
+	Savepoint* const org_save_point = transaction->tra_save_point;
+	transaction->tra_save_point = *sav_point_list;
+
+	for (Savepoint* sav_point = *sav_point_list; sav_point; sav_point = sav_point->sav_next)
 	{
 		Savepoint* const sav_next = sav_point->sav_next;
 		const SLONG sav_number = sav_point->sav_number;
 
-		// add it to the front
-
-		sav_point->sav_next = transaction->tra_save_point;
-		transaction->tra_save_point = sav_point;
+		if (!sav_point->sav_next)
+		{
+			sav_point->sav_next = org_save_point;
+		}
 
 		VIO_verb_cleanup(tdbb, transaction);
 
@@ -2155,6 +2157,8 @@ void VIO_merge_proc_sav_points(thread_db* tdbb,
 		*sav_point_list = sav_point;
 		sav_point_list = &sav_point->sav_next;
 	}
+
+	fb_assert(org_save_point == transaction->tra_save_point);
 }