minetest.get_content_id: error if the node does not exist (#9458)

If a mod creator makes a typing mistake, this function now causes an error instead of returning the id of "ignore".

src/script/lua_api/l_item.cpp

@@ -612,9 +612,11 @@ int ModApiItemMod::l_get_content_id(lua_State *L)
 	std::string name = luaL_checkstring(L, 1);
 
 	const NodeDefManager *ndef = getGameDef(L)->getNodeDefManager();
-	content_t c = ndef->getId(name);
+	content_t content_id;
+	if (!ndef->getId(name, content_id))
+		throw LuaError("Unknown node: " + name);
 
-	lua_pushinteger(L, c);
+	lua_pushinteger(L, content_id);
 	return 1; /* number of results */
 }