core,w32: Avoid recursive use of npth_unprotect.
* src/w32-estream.c (reader): Use standard free. (writer): Ditto.
There are two errors: The minor one is that we allocated with calloc
but released with _gpgrt_free. The major one is the recursive use of
npth_unprotect due to the syscall_clamp mechanism:
- Around the call to _gpgrt_w32_poll
- By gpgrt_lock_lock on behalf of a the custom allocation handler in the worker threads at their _gpgrt_free.
This problem was exhibited by GnuPG's dirmngr component.
- GnuPG-bug-id: T3937
- Signed-off-by: Werner Koch <firstname.lastname@example.org>