Fix bad window rendering with maximize-on-launch.

I have no idea why MainWindow is ruined completely in case you call
MainWindow::show, MainWindow::setWindowState(maximized) and then
in the same context (without crl::on_main) create full screen viewer.

Telegram/SourceFiles/window/window_controller.h

@@ -34,7 +34,7 @@ public:
 		return _sessionController.get();
 	}
 
-	void firstShow();
+	void finishFirstShow();
 
 	void setupPasscodeLock();
 	void clearPasscodeLock();