This commit fixes a NULL pointer dereference triggered in
spa_vdev_remove_top_check() by trying to "zpool remove" an indirect
vdev.
Reviewed-by: Matt Ahrens <matt@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes#9327