Fix if statement with empty body.

I get the following warning message :scream: :  
```
modules/multiscript/register_types.cpp:30:26: warning: if statement has empty body [-Wempty-body]
```

in line 30 of `modules/multiscript/register_types.cpp`:

```1
if (script_multi_script); // WARNING
		memdelete(script_multi_script);
```