Fix initialization of fake LSN for unlogged relations

9155580 has changed the value of the first fake LSN for unlogged
relations from 1 to FirstNormalUnloggedLSN (aka 1000), GiST requiring a
non-zero LSN on some pages to allow an interlocking logic to work, but
its value was still initialized to 1 at the beginning of recovery or
after running pg_resetwal.  This fixes the initialization for both code
paths.

Author: Takayuki Tsunakawa
Reviewed-by: Dilip Kumar, Kyotaro Horiguchi, Michael Paquier
Discussion: https://postgr.es/m/OSBPR01MB2503CE851940C17DE44AE3D9FE6F0@OSBPR01MB2503.jpnprd01.prod.outlook.com
Backpatch-through: 12

Author: michaelpq

src/backend/access/transam/xlog.c

@@ -6687,7 +6687,7 @@ StartupXLOG(void)
 	if (ControlFile->state == DB_SHUTDOWNED)
 		XLogCtl->unloggedLSN = ControlFile->unloggedLSN;
 	else
-		XLogCtl->unloggedLSN = 1;
+		XLogCtl->unloggedLSN = FirstNormalUnloggedLSN;
 
 	/*
 	 * We must replay WAL entries using the same TimeLineID they were created

src/bin/pg_resetwal/pg_resetwal.c

@@ -699,7 +699,7 @@ GuessControlValues(void)
 	ControlFile.state = DB_SHUTDOWNED;
 	ControlFile.time = (pg_time_t) time(NULL);
 	ControlFile.checkPoint = ControlFile.checkPointCopy.redo;
-	ControlFile.unloggedLSN = 1;
+	ControlFile.unloggedLSN = FirstNormalUnloggedLSN;
 
 	/* minRecoveryPoint, backupStartPoint and backupEndPoint can be left zero */