Fix memory leak in ibus-ui-gtk3

[ers35]

get_global_engine() returns a new object with a reference count of 1. Vala
adds another reference because "new IBus.EngineDesc()" isn't used. Remove the
additional reference so the engine is eventually freed.

Valgrind:

22,555 (4,160 direct, 18,395 indirect) bytes in 65 blocks are definitely lost in loss record 8,904 of 8,914
   at 0x733B3E7: g_type_create_instance (gtype.c:1845)
   by 0x731CCD7: g_object_constructor (gobject.c:2068)
   by 0x731D028: g_object_new_with_custom_constructor (gobject.c:1701)
   by 0x731D028: g_object_new_internal (gobject.c:1781)
   by 0x731EC0C: g_object_newv (gobject.c:1930)
   by 0x731F3C3: g_object_new (gobject.c:1623)
   by 0x68F5FDB: ibus_serializable_deserialize (ibusserializable.c:292)
   by 0x690AF7B: ibus_bus_get_global_engine (ibusbus.c:2002)
   by 0x120E2A: panel_real_state_changed (panel.c:5371)
   by 0x7317F74: g_closure_invoke (gclosure.c:804)
   by 0x732A37C: signal_emit_unlocked_R (gsignal.c:3673)
   by 0x7332BCB: g_signal_emit_valist (gsignal.c:3391)
   by 0x7332FAE: g_signal_emit (gsignal.c:3447)

[fujiwarat]

Thank you for the patch.
I think unowned should be used here.
unowned IBus.EngineDesc engine = m_bus.get_global_engine();

[ers35]

Won't unowned turn off reference counting and the engine will never be freed?

[fujiwarat]

You're right.
And then I think it's an annotation problem.
The get_global_engine() should be '(transfer full)':
https://github.com/ibus/ibus/blob/master/src/ibusbus.h