Update new file's prevFile pointer correctly
Update new file's prevFile pointer correctly

While updating the prevFile pointer of the next file in
the chain, update the pointer iff the next file points
to the current file.

Change-Id: Iab382c87deec3bb57f1fdf70ea3915d41d000959
Reviewed-on: http://review.couchbase.org/66174
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Chiyoung Seo <fcffc23db27b19ee4ebba46695ee6b50e09216a2@couchbase.com>

hisundar/forestdb,wurikiji/forestdb,hisundar/forestdb,wurikiji/forestdb,couchbase/forestdb,couchbase/forestdb