Fix minor logic errors

Fix minor logic errors

In k5_externalize_auth_context(), serialize the correct field when
remote_port is set.  This is not a reachable bug because the function
is only accessible via gss_export_sec_context(), and the GSS library
does not set a remote port.

In generic_gss_oid_to_str(), remove an inconsistently-applied test for
a null minor_status.  Also remove minor_status null checks from
generic_gss_release_oid() and generic_gss_str_to_oid(), but add output
initializations and pointer checks to the API functions in g_oid_ops.c
in a similar manner to other GSSAPI functions.  Remove
gssint_copy_oid_set() and replace its one call with a call to
generic_gss_copy_oid_set().

In the checksum functions, avoid crashing if the caller passes a null
key and checksum type 0.  An error will be returned instead when
find_cksumtype() can't find the checksum type.
(krb5_k_verify_checksum() already had this check.)

In pkinit_open_session(), remove an unnecessary null check for
ctx->p11_module_name, and add a check for p11name being null due to an
asprintf() failure.

In profile_add_node(), add a check for null ret_node in the duplicate
subsection check.  This is not a reachable bug because the function is
currently never called with null ret_node and null value.

In ksu's main(), check for krb5_cc_default_name() returning NULL
(which only happens on allocation failure).  Also clean up some
vestiges left behind by commit
9ebae7cb434b9b177c0af85c67a6d6267f46bc68.

In ksu's get_authorized_princ_names(), close login_fp if we fail to
open k5users_path.

In the KDC and kpropd write_pid_file(), avoid briefly leaking the file
handle on write failure.

Reported by Valery Fedorenko.