flash-one.sh: tolerate umount when nothing is mounted

scripts/flash-one.sh

@@ -43,7 +43,7 @@ echo ",+" | sfdisk --no-reread -N 2 /dev/$DEV
 for i in $(seq 1 10); do
     partprobe /dev/$DEV 2>/dev/null || true
     udevadm settle 2>/dev/null || true
-    umount /dev/${DEV}1 /dev/${DEV}2 2>/dev/null
+    umount /dev/${DEV}1 /dev/${DEV}2 2>/dev/null || true
     SIZE2=$(blockdev --getsize64 /dev/${DEV}2 2>/dev/null || echo 0)
     [ "$SIZE2" -gt 200000000000 ] && break
     sleep 1
@@ -57,7 +57,7 @@ B=/mnt/planck-boot
 R=/mnt/planck-root
 mkdir -p $B $R
 for i in 1 2 3; do
-    umount /dev/${DEV}1 /dev/${DEV}2 2>/dev/null
+    umount /dev/${DEV}1 /dev/${DEV}2 2>/dev/null || true
     mount /dev/${DEV}1 $B 2>/dev/null && mount /dev/${DEV}2 $R 2>/dev/null && break
     sleep 2
 done