Allow dns hook to fail a resolve and add domains

This lets people with crap ISPs that resolve domains
that they shouldn't to use the game without
changing their DNS server

hooklib/dns.h

@@ -4,5 +4,6 @@
 
 #include <stddef.h>
 
+// if to_src is NULL, all lookups for from_src will fail
 HRESULT dns_hook_push(const wchar_t *from_src, const wchar_t *to_src);