Replaced vector container for SendFilesBox::Block with deque.

SendFilesBox::Block (aka Block) passes action
callbacks to AlbumPreview / SingleMediaPreview.
These callbacks access Block::_items through a captured "this" pointer.

With std::vector<Block>, _blocks.emplace_back() may reallocate and
move existing Block objects. Callbacks already stored inside previews
then keep a dangling Block*, and a later context-menu action can crash
when reading this->_items.

Switched _blocks to std::deque<Block> so existing element addresses stay
stable on std::deque::push_back, keeping callback captures valid
for previews.

Telegram/SourceFiles/boxes/send_files_box.h

@@ -307,7 +307,7 @@ private:
 
 	object_ptr<Ui::ScrollArea> _scroll;
 	QPointer<Ui::VerticalLayout> _inner;
-	std::vector<Block> _blocks;
+	std::deque<Block> _blocks;
 	Fn<void()> _whenReadySend;
 	bool _preparing = false;