Fix the control flow of GroupCallView render function

2bb5b020e6 refactored the end of the GroupCallView render function to not use any early returns, and clumsily failed to account for the fall-through case that makes returnToLobby work (as opposed to sitting on a blank screen).

src/room/GroupCallView.tsx

@@ -495,9 +495,7 @@ export const GroupCallView: FC<Props> = ({
     }
   } else if (left && widget !== null) {
     // Left in widget mode:
-    if (!returnToLobby) {
-      body = null;
-    }
+    body = returnToLobby ? lobbyView : null;
   } else if (preload || skipLobby) {
     body = null;
   } else {