Fix freebsd-update(8) erroneous message and exit status when "fetch install" used.

PR:		190660
Reviewed by:	allanjude
Approved by:	emaste
Differential Revision:	https://reviews.freebsd.org/D12037

usr.sbin/freebsd-update/freebsd-update.sh

@@ -418,6 +418,9 @@ init_params () {
 
 	# Run without a TTY
 	NOTTYOK=0
+
+	# Fetched first in a chain of commands
+	ISFETCHED=0
 }
 
 # Parse the command line
@@ -783,8 +786,10 @@ install_check_params () {
 	# Check that we have updates ready to install
 	if ! [ -L ${BDHASH}-install ]; then
 		echo "No updates are available to install."
-		echo "Run '$0 fetch' first."
-		exit 1
+		if [ $ISFETCHED -eq 0 ]; then
+			echo "Run '$0 fetch' first."
+		fi
+		exit 0
 	fi
 	if ! [ -f ${BDHASH}-install/INDEX-OLD ] ||
 	    ! [ -f ${BDHASH}-install/INDEX-NEW ]; then
@@ -3241,6 +3246,7 @@ cmd_fetch () {
 	fi
 	fetch_check_params
 	fetch_run || exit 1
+	ISFETCHED=1
 }
 
 # Cron command.  Make sure the parameters are sensible; wait