Fixes bug when VM has no nic (eg in Expunging state) (closes Issue #4)

Author: Frank Louwers

lib/knife-cloudstack/connection.rb

@@ -114,6 +114,9 @@ def get_server_public_ip(server, cached_rules=nil, cached_nat=nil)
       if ip_addr
         return ip_addr['ipaddress']
       end
+      if nic.empty?
+        return []
+      end
       nic['ipaddress'] || []
     end