Fix "I will return" button

When temporarly leaving a multiplayer game the "I will return" button
didn't work. This was because there was no valid `closeSession`.
Since it requires accessing `this` the function can't be an arrow
function anymore.

Introduced in 2520c45220

Fixes: #9086

binaries/data/mods/public/gui/session/message_box/QuitConfirmationMenu.js

@@ -74,9 +74,9 @@ QuitConfirmationMenu.prototype.MultiplayerClient.prototype.Buttons =
 		},
 		{
 			"caption": translate("Yes"),
-			"onPress": closeSession =>
+			"onPress": function()
 			{
-				(new ReturnQuestion()).display(closeSession);
+				(new ReturnQuestion()).display(this.closeSession);
 			}
 		}
 	];