Fix contract violation in shutdown with webview.

Telegram/SourceFiles/core/application.cpp

@@ -63,6 +63,7 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #include "storage/storage_domain.h"
 #include "storage/storage_databases.h"
 #include "storage/localstorage.h"
+#include "payments/payments_checkout_process.h"
 #include "export/export_manager.h"
 #include "window/window_session_controller.h"
 #include "window/window_controller.h"
@@ -149,6 +150,15 @@ Application::~Application() {
 	_window = nullptr;
 	_mediaView = nullptr;
 	_notifications->clearAllFast();
+
+	// We must manually destroy all windows before going further.
+	// DestroyWindow on Windows (at least with an active WebView) enters
+	// event loop and invoke scheduled crl::on_main callbacks.
+	//
+	// For example Domain::removeRedundantAccounts() is called from
+	// Domain::finish() and there is a violation on Ensures(started()).
+	Payments::CheckoutProcess::ClearAll();
+
 	_domain->finish();
 
 	Local::finish();

Telegram/SourceFiles/payments/payments_checkout_process.cpp

@@ -112,6 +112,10 @@ bool CheckoutProcess::TakePaymentStarted(
 	return true;
 }
 
+void CheckoutProcess::ClearAll() {
+	Processes.clear();
+}
+
 void CheckoutProcess::RegisterPaymentStart(
 		not_null<CheckoutProcess*> process) {
 	const auto i = Processes.find(process->_session);

Telegram/SourceFiles/payments/payments_checkout_process.h

@@ -54,6 +54,7 @@ public:
 		Fn<void()> reactivate);
 	[[nodiscard]] static bool TakePaymentStarted(
 		not_null<const HistoryItem*> item);
+	static void ClearAll();
 
 	CheckoutProcess(
 		not_null<PeerData*> peer,

Telegram/SourceFiles/payments/ui/payments_panel.cpp

@@ -501,7 +501,7 @@ bool Panel::createWebview() {
 			_webview = nullptr;
 			if (_webviewProgress) {
 				hideWebviewProgress();
-				if (!_progress->shown) {
+				if (_progress && !_progress->shown) {
 					_progress = nullptr;
 				}
 			}