dirmngr: Avoid accessing uninitialized memory in log callback.

* dirmngr/dirmngr.c (pid_suffix_callback): Clear int_and_ptr_u before
use.
(start_connection_thread): Ditto.
(handle_connections): Ditto.

Example valgrind output:

2921== Conditional jump or move depends on uninitialised value(s)

2921== at 0x5BBDEF4: pthread_getspecific (pthread_getspecific.c:57)

2921== by 0x40AAEE: pid_suffix_callback (dirmngr.c:614)

2921== by 0x433F5A: do_logv (logging.c:684)

This is because on 64 bit systems "sizeof aptr > sizeof aint" and thus
Valgrind complains about this. It is no a real problem because we
don't use the unitialized bits.

• Signed-off-by: Werner Koch <wk@gnupg.org>