iomgr: Remove crash when host cannot be parsed

The crash isn't exactly very helpful, and there's a "Good" workaround
for this.

Change-Id: I50579a6c84441d704011f79b45f55c40ce8fb7cb
Reviewed-on: http://review.couchbase.org/44131
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>