Fix URL previews being enabled when room first created (#8227)

We didn't update whether URL previews should be enabled when encryption
was enabled in a room, so when you create a room (or enable encryption)
it starts off with URL previews using the setting for non-e2e rooms
untilyou switch rooms / refresh.

src/components/structures/RoomView.tsx

@@ -944,6 +944,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
 
         if (ev.getType() === "m.room.encryption") {
             this.updateE2EStatus(room);
+            this.updatePreviewUrlVisibility(room);
         }
 
         // ignore anything but real-time updates at the end of the room: