ntlm: Fixed empty type-2 decoded message info text

Updated the info text when the base-64 decode of the type-2 message
returns a null buffer to be more specific.

lib/curl_ntlm_msgs.c

@@ -292,7 +292,7 @@ CURLcode Curl_ntlm_decode_type2_message(struct SessionHandle *data,
     return error;
 
   if(!buffer) {
-    infof(data, "NTLM handshake failure (unhandled condition)\n");
+    infof(data, "NTLM handshake failure (empty type-2 message)\n");
     return CURLE_BAD_CONTENT_ENCODING;
   }