Fix JitsiConference access

With so many abstractions called conference, I'm not surprised I made a
mistake and my reviewer didn't catch it.

As we are transitioning from remote participants identified by ID alone
to an ID-conference pair, the subsequent commits "Protect against late
PARTICIPANT_JOINED" and "Refine PARTICIPANT_LEFT for ID collisions"
caught the error.

modules/UI/shared_video/SharedVideo.js

                 SHARED_VIDEO_CONTAINER_TYPE, self.sharedVideo);
 
             APP.store.dispatch(participantJoined({
-                conference: APP.conference,
+
+                // FIXME The cat is out of the bag already or rather _room is
+                // not private because it is used in multiple other places
+                // already such as AbstractPageReloadOverlay and
+                // JitsiMeetLogStorage.
+                conference: APP.conference._room,
                 id: self.url,
                 isBot: true,
                 name: 'YouTube'
                     UIEvents.UPDATE_SHARED_VIDEO, null, 'removed');
             });
 
-        APP.store.dispatch(participantLeft(this.url, APP.conference));
+        APP.store.dispatch(participantLeft(this.url, APP.conference._room));
 
         this.url = null;
         this.isSharedVideoShown = false;

react/features/base/participants/actions.js

 
 import throttle from 'lodash/throttle';
 
+import { set } from '../redux';
 import { showNotification } from '../../notifications';
 
 import {
  * }}
  */
 export function localParticipantJoined(participant = {}) {
-    return participantJoined({
-        ...participant,
-        local: true
-    });
+    return participantJoined(set(participant, 'local', true));
 }
 
 /**