fix: optimization: PVS-Studio warning V821

Creating variables in a more localized scope can enhance performance and make the code easier to understand.

Reported by: PVS-Studio
Signed-off-by: Vyacheslav Ivanov <islavaivanov76@gmail.com>

src/frontend/hud.cpp

@@ -406,9 +406,9 @@ void Hud::add(const HudElement& element) {
     using namespace dynamic;
 
     gui->add(element.getNode());
-    auto invview = std::dynamic_pointer_cast<InventoryView>(element.getNode());
     auto document = element.getDocument();
     if (document) {
+        auto invview = std::dynamic_pointer_cast<InventoryView>(element.getNode());
         auto inventory = invview ? invview->getInventory() : nullptr;
         std::vector<Value> args;
         args.emplace_back(inventory ? inventory.get()->getId() : 0);