Use luaL_checkstring in set_style

src/lua/lua_theme.cpp

@@ -24,13 +24,11 @@ namespace lua {
 
 static auto set_style(lua_State* L) -> int {
   // Get the object and class name from the stack
-  if (lua_type(L, -1) == LUA_TSTRING) {
-    std::string class_name = lua_tostring(L, -1);
+  std::string class_name = luaL_checkstring(L, -1);
   lv_obj_t* obj = luavgl_to_obj(L, -2);
   if (obj != NULL) {
     ui::themes::Theme::instance()->ApplyStyle(obj, class_name);
   }
-  }
   return 0;
 }