Should casting a char * to _Nt_array_ptr be allowed?

[secure-sw-dev-bot]

This issue was copied from checkedc/checkedc-clang#1155

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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.