heartbleed - Better output on wrong jabber domain and add. nil? check

modules/auxiliary/scanner/ssl/openssl_heartbleed.rb

@@ -184,10 +184,14 @@ class Metasploit3 < Msf::Auxiliary
     sock.put(msg)
     # get first response with id
     res = sock.get_once
-    return nil if res.nil? # SSL not supported
+    if res.nil? || res =~ /stream:error/
+      # check for unknown host error message
+      print_error("#{peer} - Jabber host unknown. Please try changing the XMPPDOMAIN option.") if res =~ /<host-unknown/
+      return nil
+    end
     # get next part of the message
     res = sock.get_once
-    return nil if res =~ /stream:error/ || res !~ /starttls/i
+    return nil if res.nil? || res =~ /stream:error/ || res !~ /starttls/i
     msg = "<starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>"
     sock.put(msg)
     sock.get_once