dlm: handle invalid lockspace member remove

dlm: handle invalid lockspace member remove

Since commit de7b4869b4ecf ("dlm: add new configfs entry release_recover
for lockspace members") we are moving lockspace members into a gone list
before removing them to get additional removing attributes from
configfs. There is still a very unlikely possibility when
find_config_node() returns NULL, then for some reason the node wasn't
marked as gone but it was removed. We will just handle this case and drop
an error to observe if this case can ever happen.

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/gfs2/aJ2Ssuh8xlsTutrA@stanley.mountain/T/#u
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>