Add VALIDATE_LUA as a function in lpxserver and lpxclient

luprex/cpp/core/world-core.cpp

@@ -377,14 +377,10 @@ eng::string World::probe_lua_expr(int64_t actor_id, std::string_view lua) {
 
     LuaVar closure;
     LuaExtStack LS(L, closure);
-
-    // create the compiled closure.
-    int status = luaL_loadbuffer(L, lua.data(), lua.size(), "=probe");
-    lua_replace(L, closure.index());
-    if (status != LUA_OK) {
-        // The closure is actually an error message. Do nothing.
-        // This should normally not happen: LuaConsole should filter
-        // out syntax errors.
+    eng::string errmsg = LS.load(closure, lua, "probe");
+    if (!errmsg.empty()) {
+        // This should normally not happen: the front end should
+        // filter expressions for syntactic lua validity.
         return "";
     }