[Bug c++/60168] Incorrect check in ~unique_ptr() when Deleter::pointer type is not a pointer type

[ashish.sadanandan at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60168

--- Comment #3 from Ashish Sadanandan <ashish.sadanandan at gmail dot com> ---
You are right, of course. Not a bug, but it's disappointing that it isn't. If
that comparison were against a value initialized unique_ptr<T, D>::pointer,
instead of nullptr, it'd allow unique_ptr to be used to manage any generic
`handle` type, which may not meet the requirements of NullablePointer.