If `numResult == 0` or `func == nullptr`, you return `0` directly.
```
if (traceCallback)
 +        {
 +            lua_pop(_state, 1);                                          // remove __G__TRACKBACK__ from stack      /* L: ... */
 +        }
 +    }
 +    
 +    lua_settop(_state, 0);
```

will not be invoked.

Maybe it will cause some stack problems.