fix(message): prevent segfault on invalid UTF-8 - #624

==15189== Process terminating with default action of signal 11 (SIGSEGV): dumping core
==15189==  Access not within mapped region at address 0x8
==15189==    at 0x49AACAC: Py_TYPE (object.h:336)
==15189==    by 0x49AACAC: Py_IS_TYPE (object.h:369)
==15189==    by 0x49AACAC: _PyObject_HashFast (pycore_object.h:732)
==15189==    by 0x49AACAC: PyDict_Contains (dictobject.c:4706)
==15189==    by 0x13FD2262: LDAPmessage_to_python (message.c:101)
==15189==    by 0x13FD31AC: l_ldap_result4 (LDAPObject.c:1186)

==15073== Process terminating with default action of signal 11 (SIGSEGV): dumping core
==15073==  Access not within mapped region at address 0x0
==15073==    at 0x13FD2864: _Py_IsImmortal (object.h:361)
==15073==    by 0x13FD2864: Py_DECREF (object.h:944)
==15073==    by 0x13FD2864: LDAPmessage_to_python (message.c:226)
==15073==    by 0x13FD31AC: l_ldap_result4 (LDAPObject.c:1186)

#!/usr/bin/env python3


import socket
import threading
import time

import ldap

# msgid=1, SearchResultEntry: DN="", one attribute, type="\x93", empty value set
ENTRY = bytes([
    0x30, 0x10,          # SEQUENCE, len 16
    0x02, 0x01, 0x01,    #   msgid = 1
    0x64, 0x0b,          #   [APP 4] SearchResultEntry, len 11
    0x04, 0x00,          #     DN = ""
    0x30, 0x07,          #     attributes SEQUENCE, len 7
    0x30, 0x05,          #       attr SEQUENCE, len 5
    0x04, 0x01, 0x93,    #         type = "\x93" (invalid UTF-8)
    0x31, 0x00,          #         vals SET (empty)
])

# msgid=1, SearchResultReference: single URL "\x93"
REF = bytes([
    0x30, 0x08,          # SEQUENCE, len 8
    0x02, 0x01, 0x01,    #   msgid = 1
    0x73, 0x03,          #   [APP 19] SearchResultReference, len 3
    0x04, 0x01, 0x93,    #     URL = "\x93"
])

DONE = bytes([
    0x30, 0x0c, 0x02, 0x01, 0x01, 0x65, 0x07,
    0x0a, 0x01, 0x00, 0x04, 0x00, 0x04, 00,
])


def serve(srv):
    conn, _ = srv.accept()
    conn.recv(4096)
    conn.sendall(REF + DONE) # another error place
    # conn.sendall(ENTRY + DONE)
    time.sleep(2)
    conn.close()


def main():
    srv = socket.socket()
    srv.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    srv.bind(("127.0.0.1", 0))
    srv.listen(1)
    threading.Thread(target=serve, args=(srv,), daemon=True).start()

    conn = ldap.initialize(f"ldap://127.0.0.1:{srv.getsockname()[1]}/")
    conn.search_ext_s("dc=example,dc=com", ldap.SCOPE_SUBTREE, 
                      "(objectClass=*)", ["*"])
    print("no crash — bug fixed?")


if __name__ == "__main__":
    main()