Should casting a char * to _Nt_array_ptr be allowed?

Should we allow this type of code?
```
char *g(_Nt_array_ptr<char> p);

void f(_Nt_array_ptr<char> p) {
  p = (_Nt_array_ptr<char>) g(p);
}
```

There is no guarantee that the `char *` returned by the function `g()` actually contains a null-terminator.