Move ShutdownXLOG() to checkpoint process

BgWriter no more has pendingOpsTable, hence it should not call the
CreateCheckPoint() directly.

Error message was introduced in upstream
ef072219, and the refactoring of ShutdownXLOG()
was introduced in upstream 806a2aee.

src/backend/postmaster/bgwriter.c

@@ -316,8 +316,6 @@ BackgroundWriterMain(void)
 			 * control back to the sigsetjmp block above
 			 */
 			ExitOnAnyError = true;
-			/* Close down the database */
-			ShutdownXLOG(0, 0);
 			DumpFreeSpaceMap(0, 0);
 
 			/* Normal exit from the bgwriter server is here */

src/backend/postmaster/checkpoint.c

@@ -361,6 +361,8 @@ CheckpointMain(void)
 			 * control back to the sigsetjmp block above
 			 */
 			ExitOnAnyError = true;
+			/* Close down the database */
+			ShutdownXLOG(0, 0);
 
 			/* Normal exit from the checkpoint server is here */
 			if (Debug_print_server_processes ||