LU-8001 nodemap: fix null deref when reclassifying

LU-8001 nodemap: fix null deref when reclassifying

There are some situations in which an export's connection can be
NULL. This patch adds a NULL check before dereferencing in
nm_member_reclassify_nodemap. If the connection is null, keep export
in current nodemap since it should get reclassified on reconnect.

Signed-off-by: Kit Westneat <kit.westneat@gmail.com>
Change-Id: I795afdac3b388e883bafe5a79c8237794bc01ef6
Reviewed-on: http://review.whamcloud.com/19595
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>