Fix email registration

This would cause the request to 400 in the new vector that opens after you clicked the link in the email, as per the comment.

lib/client.js

@@ -2423,11 +2423,20 @@ MatrixClient.prototype.register = function(username, password,
  * @return {module:http-api.MatrixError} Rejects: with an error response.
  */
 MatrixClient.prototype.registerRequest = function(data, kind, callback) {
-    var request_data = {
+    var request_data = {};
+
+    // only add these if the app is sending something other than auth data
+    // subsequent calls to register with the same session will
+    // overwrite the parameters if any are passed, so it's important
+    // that if the app give no data, we send no data.
+    var number_of_params = Object.keys(data).length;
+    if (data.auth) --number_of_params;
+    if (number_of_params > 0) {
+        request_data = {
             device_id: this.deviceId,
             initial_device_display_name: this.defaultDeviceDisplayName,
         };
-
+    }
     // merge data into request_data
     for (var k in data) {
         if (data.hasOwnProperty(k)) { request_data[k] = data[k]; }