dbus: Fix invalid read at method reply
dbus: Fix invalid read at method reply

This patch fixes the following error when Forget() gets called:
knotd[28680]: Proxy for 123456789 removed
==28680== Invalid read of size 8
==28680==    at 0x112035: method_reply (device.c:102)
==28680==    by 0x52D9854: handle_error.isra.1 (dbus.c:216)
==28680==    by 0x52DA94B: message_read_handler (dbus.c:276)
==28680==    by 0x52D4668: io_callback (io.c:127)
==28680==    by 0x52D39AD: l_main_iterate (main.c:381)
==28680==    by 0x52D3A7B: l_main_run (main.c:428)
==28680==    by 0x10C84A: l_main_loop_run (main.c:83)
==28680==    by 0x10CA3F: main (main.c:149)

CESARBR/knot-service-source,CESARBR/knot-service-source,CESARBR/knot-service-source,CESARBR/knot-service-source,CESARBR/knot-service-source