refactor: PVS-Studio warnings fixes

src/logic/scripting/lua/libitem.cpp

@@ -4,12 +4,9 @@
 
 using namespace scripting;
 
-static ItemDef* get_item_def(lua::State* L, int idx) {
+static const ItemDef* get_item_def(lua::State* L, int idx) {
     auto indices = content->getIndices();
     auto id = lua::tointeger(L, idx);
-    if (static_cast<size_t>(id) >= indices->items.count()) {
-        return nullptr;
-    }
     return indices->items.get(id);
 }