iocp: don't requeue overlapped if stop_loop is called

While this might have good intentions, the ordering of operations --
namely read operations is important. If we repost an event we'd also
need to reorder everything.

I just happened to notice this while looking about :)

Change-Id: I4c542ab792db7f450e325a12b5f39d0135a0fe2a
Reviewed-on: http://review.couchbase.org/38329
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>