CCBC-182 Fix mistyped condition in the loop

The library stops iterating backup nodes list if next one isn't
accessible

Change-Id: Ia583257f6d8291e468bf23a983738c9e2f52c7d4
Reviewed-on: http://review.couchbase.org/24623
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>