Fix crash in SelfDestructionBox.

base::lambda_guarded may destroy the lambda after the owner. In case
of SelfDestructionBox it lead to a dtor of a dangling object_ptr.

MTP::Sender destroys the lambda handlers together with itself.

Telegram/SourceFiles/boxes/self_destruction_box.cpp

@@ -44,7 +44,7 @@ void SelfDestructionBox::prepare() {
 
 	addButton(lang(lng_cancel), [this] { closeBox(); });
 
-	MTP::send(MTPaccount_GetAccountTTL(), rpcDone(base::lambda_guarded(this, [this, loading = std::move(loading)](const MTPAccountDaysTTL &result) mutable {
+	request(MTPaccount_GetAccountTTL()).done([this, loading = std::move(loading)](const MTPAccountDaysTTL &result) mutable {
 		Expects(result.type() == mtpc_accountDaysTTL);
 		Expects(!_ttlValues.empty());
 
@@ -77,5 +77,5 @@ void SelfDestructionBox::prepare() {
 			closeBox();
 		});
 		addButton(lang(lng_cancel), [this] { closeBox(); });
-	})));
+	}).send();
 }

Telegram/SourceFiles/boxes/self_destruction_box.h

@@ -21,14 +21,15 @@ Copyright (c) 2014-2017 John Preston, https://desktop.telegram.org
 #pragma once
 
 #include "boxes/abstractbox.h"
+#include "mtproto/sender.h"
 
 namespace Ui {
 class RadiobuttonGroup;
 class Radiobutton;
 class FlatLabel;
 } // namespace Ui
 
-class SelfDestructionBox : public BoxContent {
+class SelfDestructionBox : public BoxContent, private MTP::Sender {
 	Q_OBJECT
 
 public: