Null exception when casting with inheritance of depth 2+

Casting a subclass of a subclass to their base class will cause a strange "null" exception at line 0 of a random external/standard library.

```haxe
abstract class A {
public abstract function work():Void;
}

abstract class B extends A {

public abstract function work(): Void;
}

class C extends B {
public function new() {}

public function work():Void {
trace("doing");
}
}

class Main {

static function main(){
var c = new C();
var a: A = cast c;
a.work();
}
}
```

Result:

Called from A.work(C:\HaxeToolkit\haxe\std/hl/_std/Date.hx:0)
Called from $Main.main(Main.hx:24)
Called from .init(?:1)

As you can see it strangely fails at "Date.hx:0". Casting to Dynamic instead can be used as a workaround.

The above code snippet works in other targets.