Initramfs zfs script error when pool previously imported

[jose-pr]

Describe the problem you're observing

When you run zfs with initramfs and have a previous script import the pool, in my case to unlock it with a custom method to get the key, initramfs will drop you in a shell as the the zfs mountscripts doens't doesnt update POOL_IMPORTED

Describe how to reproduce the problem

Have a scripts in initramfs that call import on the root pool, before or during local.premount

zpool import -N rpool

Problem seem to happen here: https://github.com/openzfs/zfs/blob/04bae5ec95f7273105237159a882d5b72ec2b998/contrib/initramfs/scripts/zfs#L197C1-L198C1

	"${ZPOOL}" get -H -o value name,guid 2>/dev/null | grep -Fxq "$pool" && return 0

Where it knows pool is imported but return without setting POOL_IMPORTED and then it goes to find the find_rootfs and errors out.

Would suggest something along the lines of:

if "${ZPOOL}" get -H -o value name,guid 2>/dev/null | grep -Fxq "$pool"; then
  POOL_IMPORTED=1
  return 0
fi