Handle errors while opening a Websocket

For example, previously if the user typed in illegal characters in the
port field, no error would be displayed in the interface and the page
would stop at "connecting".

core/rfb.js

@@ -372,7 +372,15 @@
             uri += '://' + this._rfb_host + ':' + this._rfb_port + '/' + this._rfb_path;
             Util.Info("connecting to " + uri);
 
+            try {
                 this._sock.open(uri, this._wsProtocols);
+            } catch (e) {
+                if (e.name === 'SyntaxError') {
+                    this._fail("Invalid host or port value given");
+                } else {
+                    this._fail("Error while opening websocket (" + e + ")");
+                }
+            }
 
             Util.Debug("<< RFB.connect");
         },