Fixed bug with empty domain directive.

Backpatched from 0.6:1.29.

Rev: lib/modules/Protocols.pmod/DNS.pmod:1.30

lib/modules/Protocols.pmod/DNS.pmod

@@ -341,6 +341,7 @@ class client {
       }
       if(domain)
 	domains = ({ domain }) + domains;
+      domains -= ({ "" });
       domains = Array.map(domains, lambda(string d) {
 				     if (d[-1] == '.') {
 				       return d[..sizeof(d)-2];