core,w32: Fix missing sentinel in dir name builder.
core,w32: Fix missing sentinel in dir name builder.

* src/w32-util.c (_gpgme_get_gpgconf_path): Add NULL top strconcat.
--

Fortunately this is called early and the stack like cleared out so
that we have not seen wrong behaviour until now.  We should really fix
all these annoying HANDLE/int cast warnings and alike so that real
bugs are not drowned by them.

GnuPG-bug-id: 4369
Signed-off-by: Werner Koch <13bd1fc5137f503b0a8355ad400e7a87ebb45b25@gnupg.org>

gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme