feat(prejoin) cache media start options when on prejoin screen

react/features/prejoin/middleware.js

 // @flow
 
+import { SET_AUDIO_MUTED, SET_VIDEO_MUTED } from '../base/media';
 import { MiddlewareRegistry } from '../base/redux';
 import { updateSettings } from '../base/settings';
 import { getLocalVideoTrack, replaceLocalTrack } from '../base/tracks';
 
 import { PREJOIN_START_CONFERENCE } from './actionTypes';
 import { setPrejoinPageVisibility } from './actions';
+import { isPrejoinPageVisible } from './functions';
 
 declare var APP: Object;
 
 
         break;
     }
+
+    case SET_AUDIO_MUTED: {
+        if (isPrejoinPageVisible(store.getState())) {
+            store.dispatch(updateSettings({
+                startWithAudioMuted: Boolean(action.muted)
+            }));
+        }
+        break;
+    }
+
+    case SET_VIDEO_MUTED: {
+        if (isPrejoinPageVisible(store.getState())) {
+            store.dispatch(updateSettings({
+                startWithVideoMuted: Boolean(action.muted)
+            }));
+        }
+        break;
     }
 
+    }
 
     return next(action);
 });