Fix errors in comm.lua and nmap_dns.cc

[dksslq]

1. Fix error: attempt to call a table value

Select an http related script such as http-title. error:

/root/nmap0/nselib/comm.lua:284: attempt to call a table value (for iterator 'for iterator')
stack traceback:
        /root/nmap0/nselib/comm.lua:284: in function 'comm.tryssl'
        (...tail calls...)
        /root/nmap0/nselib/http.lua:1357: in function </root/nmap0/nselib/http.lua:1339>
        (...tail calls...)
        /root/nmap0/nselib/http.lua:1776: in function 'http.get'
        /root/nmap0/scripts/http-title.nse:39: in function </root/nmap0/scripts/http-title.nse:36>
        (...tail calls...)

Completed NSE at 16:19, 0.04s elapsed

2. Fix Infinite loop in nmap_dns.cc previous behavior: if nmap start mass_dns with a unreachable dns server(nsock_connect_udp error) then, mass_dns main loop never finish.

[nnposter]

The missing table iterator has been added in r38953.