[RN] Fix processing outdated loadConfig requests

This fix is based on storing the location URL object we are loading the
configuration for in the redux store. Once the config has been loaded (or it has
failed, for that matter!) we'll check if the current "config URL" is the same we
set, and discard the old one if they don't match.

react/features/app/actions.js

 /* @flow */
 
+import type { Dispatch } from 'redux';
+
 import { setRoom } from '../base/conference';
 import {
     configWillLoad,
      * @returns {void}
      */
     function loadConfigSettled(error, config) {
-        // FIXME Due to the asynchronous nature of the loading, the specified
+        // Due to the asynchronous nature of the loading, the specified
         // config may or may not be required by the time the notification
-        // arrives.
+        // arrives. If we receive the config for a location we are no longer
+        // interested in, just dump it.
+
+        const { locationURL: currentLocationURL }
+            = getState()['features/base/config'];
+
+        if (currentLocationURL !== newLocation) {
+            throw new Error('Config no longer needed');
+        }
 
         const promise
             = dispatch(setLocationURL(new URL(newLocation.toString())));

react/features/base/config/reducer.js

         switch (action.type) {
         case CONFIG_WILL_LOAD:
             return {
-                error: undefined
+                error: undefined,
+                locationURL: action.locationURL
             };
 
         case LOAD_CONFIG_ERROR: