Backport "Avoid closing the widget in returnToLobby mode" to v0.7

This is a manual backport of 28c45c6107 which makes the video room behavior consistent across the v0.7.2 patch release and development versions.

src/rtcSessionHelpers.ts

@@ -17,6 +17,7 @@ import {
 import { PosthogAnalytics } from "./analytics/PosthogAnalytics";
 import { Config } from "./config/Config";
 import { ElementWidgetActions, WidgetHelpers, widget } from "./widget";
+import { getUrlParams } from "./UrlParams";
 
 const FOCI_WK_KEY = "org.matrix.msc4143.rtc_foci";
 
@@ -144,11 +145,13 @@ const widgetPostHangupProcedure = async (
   // of Element Call will do, we additionally send a close action (even though
   // we're not yet employing the distinction between 'hangup' and 'close' to
   // display error screens)
+  if (!getUrlParams().returnToLobby) {
     try {
       await widget.api.transport.send(ElementWidgetActions.Close, {});
     } catch (e) {
       logger.error("Failed to send close action", e);
     }
+  }
 };
 
 export async function leaveRTCSession(