[select] Don't hang when timeout < now

Change-Id: I5395d4f1103a2c9187ce04fce8fce1de2125987a
Reviewed-on: http://review.couchbase.org/27986
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>