Basically in loops like handle_errors(), 'query->next' was assigned a local
variable and then query was referenced after the memory was freed by
next_server(). I've changed that so next_server() and end_query() returns the
next query. So callers should use this ret-value.

The next problem was that 'server->tcp_buffer_pos' had a random value at entry
to 1st recv() (luckily causing Winsock to return ENOBUFS).

I've also added a ares_writev() for Windows to streamline the code
a bit more.