lock the record header before fetching its backversion with delta

Author: AlexeyMochalov

src/jrd/vio.cpp

@@ -7321,6 +7321,9 @@ void VIO_update_in_place(thread_db* tdbb,
 
 	AutoTempRecord gc_rec;
 
+	if (!DPM_get(tdbb, org_rpb, LCK_write))
+		BUGCHECK(186);	// msg 186 record disappeared
+
 	record_param temp2;
 	const Record* prior = org_rpb->rpb_prior;
 	if (prior)
@@ -7347,9 +7350,6 @@ void VIO_update_in_place(thread_db* tdbb,
 		stack->push(PageNumber(pageSpaceID, temp2.rpb_page));
 	}
 
-	if (!DPM_get(tdbb, org_rpb, LCK_write))
-		BUGCHECK(186);	// msg 186 record disappeared
-
 	if (prior)
 	{
 		const ULONG page = org_rpb->rpb_b_page;