Ensure we don't do an user-after-free access, as reported by ASAN:
==3704==ERROR: AddressSanitizer: stack-use-after-return on address
0x70a58f8631c0 at pc 0x000000405144 bp 0x7fffff62c7a0 sp 0x7fffff62c798
READ of size 4 at 0x70a58f8631c0 thread T0
#0 0x405143 in on_object_unregistered ../../GNOME/glib/gio/tests/gdbus-export.c:597
#1 0x70a592e858d8 in call_destroy_notify_data_in_idle ../../GNOME/glib/gio/gdbusconnection.c:244
#2 0x70a5940016a4 in g_idle_dispatch ../../GNOME/glib/glib/gmain.c:6221
#3 0x70a59401095b in g_main_dispatch ../../GNOME/glib/glib/gmain.c:3348
#4 0x70a59401095b in g_main_context_dispatch_unlocked ../../GNOME/glib/glib/gmain.c:4197
#5 0x70a59401ba17 in g_main_context_iterate_unlocked ../../GNOME/glib/glib/gmain.c:4262
#6 0x70a59401cc73 in g_main_context_iteration ../../GNOME/glib/glib/gmain.c:4327
#7 0x405658 in test_threaded_unregistration_iteration ../../GNOME/glib/gio/tests/gdbus-export.c:1878
#8 0x405658 in test_threaded_unregistration ../../GNOME/glib/gio/tests/gdbus-export.c:1952
#9 0x70a5940dfb04 in test_case_run ../../GNOME/glib/glib/gtestutils.c:2988
#10 0x70a5940dfb04 in g_test_run_suite_internal ../../GNOME/glib/glib/gtestutils.c:3090
#11 0x70a5940df893 in g_test_run_suite_internal ../../GNOME/glib/glib/gtestutils.c:3109
#12 0x70a5940df893 in g_test_run_suite_internal ../../GNOME/glib/glib/gtestutils.c:3109
#13 0x70a5940e0bc9 in g_test_run_suite ../../GNOME/glib/glib/gtestutils.c:3189
#14 0x70a5940e0d1f in g_test_run ../../GNOME/glib/glib/gtestutils.c:2275
#15 0x40eb72 in session_bus_run ../../GNOME/glib/gio/tests/gdbus-sessionbus.c:69
#16 0x403a2c in main ../../GNOME/glib/gio/tests/gdbus-export.c:1990
#17 0x70a591d9f149 in __libc_start_call_main (/lib64/libc.so.6+0x28149) (BuildId: 0d710e9d9dc10c500b8119c85da75004183618e2)
#18 0x70a591d9f20a in __libc_start_main_impl (/lib64/libc.so.6+0x2820a) (BuildId: 0d710e9d9dc10c500b8119c85da75004183618e2)
#19 0x403b44 in _start (/tmp/_build/gio/tests/gdbus-export+0x403b44) (BuildId: f6312e919c3d94e4c49270b0dfc5c870e1ba550b)
Address 0x70a58f8631c0 is located in stack of thread T0 at offset 192 in frame
#0 0x40525f in test_threaded_unregistration ../../GNOME/glib/gio/tests/gdbus-export.c:1936
This frame has 7 object(s):
[32, 40) 'local_error' (line 1835)
[64, 72) 'unregister_thread' (line 1836)
[96, 104) 'value' (line 1838)
[128, 136) 'value_str' (line 1839)
[160, 168) 'call_result' (line 1840)
[192, 204) 'object_registration_data' (line 1834) <== Memory access at offset 192 is inside this variable
[224, 240) 'data' (line 1833)