Fix SEGFAULT after evdns_base_resume if no nameservers installed.

If there is no nameservers installed, using
evdns_base_nameserver_ip_add(), than evdns_base_resume() will SEGFAULT,
because of NULL dereference in evdns_requests_pump_waiting_queue()

Conflicts:
	evdns.c
restore the comment
Merge remote-tracking branch 'public/pr/79' into patches-2.0