This reverts commit 21a7873f.

This appears to cause a segfault, presumably resulting from something
assuming that reader_init() would not reinitialize all fields:

 #0  0x00007ffff7b74777 in _dbus_type_reader_get_current_type (reader=reader@entry=0x7fffffffda50) at .../dbus/dbus-marshal-recursive.c:791
 #1  0x00007ffff7b719d0 in _dbus_header_cache_check (header=<optimized out>)
    at .../dbus/dbus-marshal-header.c:209
 #2  0x00007ffff7b719d0 in _dbus_header_cache_check (header=header@entry=0x624658, field=field@entry=6) at .../dbus/dbus-marshal-header.c:250
 #3  0x00007ffff7b72884 in _dbus_header_get_field_basic (header=header@entry=0x624658, field=field@entry=6, type=type@entry=115, value=value@entry=0x7fffffffdbd8) at .../dbus/dbus-marshal-header.c:1365
 #4  0x00007ffff7b7d8c2 in dbus_message_get_destination (message=message@entry=0x624650) at .../dbus/dbus-message.c:3457
 #5  0x00007ffff7b67be6 in _dbus_connection_send_preallocated_unlocked_no_update (connection=connection@entry=0x6236d0, preallocated=0x0,
    preallocated@entry=0x6234c0, message=message@entry=0x624650, client_serial=client_serial@entry=0x7fffffffdcbc)
    at .../dbus/dbus-connection.c:2017