x86: move sysupgrade.tgz only if it exists

To squash error messages at boot time

    mv: can't rename '/mnt/sysupgrade.tgz': No such file or directory

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

target/linux/x86/base-files/lib/preinit/79_move_config

@@ -7,9 +7,12 @@ move_config() {
 	. /lib/upgrade/platform.sh
 
 	if platform_export_bootdevice && platform_export_partdevice partdev 1; then
-		mount -t ext4 -o rw,noatime "/dev/$partdev" /mnt
-		mv -f /mnt/sysupgrade.tgz /
-		umount /mnt
+		if mount -t ext4 -o rw,noatime "/dev/$partdev" /mnt; then
+			if [ -f /mnt/sysupgrade.tgz ]; then
+				mv -f /mnt/sysupgrade.tgz /
+			fi
+			umount /mnt
+		fi
 	fi
 }