only umount if mounted

bootrap-bullseye.sh

@@ -203,12 +203,12 @@ chroot $mnt /bin/bash -c "grub-install $disk && update-grub"
 }
 
 unmount(){
-# Unmount
-umount $mnt/proc
-umount $mnt/sys
-umount $mnt/dev/pts
-umount $mnt/dev
-umount $mnt/root
+# Unmount if mounted
+! mountpoint -q $mnt/proc    || umount $mnt/proc
+! mountpoint -q $mnt/sys     || umount $mnt/sys
+! mountpoint -q $mnt/dev/pts || umount $mnt/dev/pts
+! mountpoint -q $mnt/dev     || umount $mnt/dev
+! mountpoint -q $mnt/root    || umount $mnt/root
 }