Select: Don't call select() if there are only timers

We can sleep manually and wait for them to expire. Otherwise we get a
SOCKET_ERROR on win32 which quits the event loop

Change-Id: I71fa090662cf7e22bfd1f26d77fa0272e6a3cf1f
Reviewed-on: http://review.couchbase.org/31741
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>