[RN] Use a default host when only a room name is specified

The mobile app remembers the domain which hosted the last conference. If
the user specified a full URL first and specified a room name only the
second time, it was not obvious that the second conference would be
hosted on the domain of the first conference.

react/features/app/actions.js

  * Triggers an in-app navigation to a different route. Allows navigation to be
  * abstracted between the mobile and web versions.
  *
- * @param {(string|undefined)} urlOrRoom - The URL or room name to which to
- * navigate.
+ * @param {(string|undefined)} uri - The URI to which to navigate. It may be a
+ * full URL with an http(s) scheme, a full or partial URI with the app-specific
+ * sheme, or a mere room name.
  * @returns {Function}
  */
-export function appNavigate(urlOrRoom) {
+export function appNavigate(uri) {
     return (dispatch, getState) => {
         const state = getState();
         const oldDomain = getDomain(state);
 
-        const { domain, room } = _parseURIString(urlOrRoom);
+        // eslint-disable-next-line prefer-const
+        let { domain, room } = _parseURIString(uri);
+
+        // If the specified URI does not identify a domain, use the app's
+        // default.
+        if (typeof domain === 'undefined') {
+            domain
+                = _parseURIString(state['features/app'].app._getDefaultURL())
+                    .domain;
+
+        }
 
         // TODO Kostiantyn Tsaregradskyi: We should probably detect if user is
         // currently in a conference and ask her if she wants to close the
             dispatch(setDomain(domain));
 
             // If domain has changed, we need to load the config of the new
-            // domain and set it, and only after that we can navigate to
+            // domain and set it, and only after that we can navigate to a
             // different route.
             loadConfig(`https://${domain}`)
                 .then(
             dispatch(
                 _setRoomAndNavigate(
                     typeof room === 'undefined' && typeof domain === 'undefined'
-                        ? urlOrRoom
+                        ? uri
                         : room));
         }
     };

react/features/app/components/AbstractApp.js

 
         dispatch(localParticipantJoined());
 
-        this._openURL(this._getDefaultURL());
+        // If a URL was explicitly specified to this React Component, then open
+        // it; otherwise, use a default.
+        this._openURL(this.props.url || this._getDefaultURL());
     }
 
     /**
     /**
      * Gets the default URL to be opened when this App mounts.
      *
-     * @private
+     * @protected
      * @returns {string} The default URL to be opened when this App mounts.
      */
     _getDefaultURL() {
-        // If the URL was explicitly specified to the React Component, then open
-        // it.
-        let url = this.props.url;
-
-        if (url) {
-            return url;
-        }
-
         // If the execution environment provides a Location abstraction, then
         // this App at already at that location but it must be made aware of the
         // fact.
         const windowLocation = this._getWindowLocation();
 
         if (windowLocation) {
-            url = windowLocation.toString();
-            if (url) {
-                return url;
+            const href = windowLocation.toString();
+
+            if (href) {
+                return href;
             }
         }