Fix GSocketAddress leak in proxy_lookup_ready()
Fix GSocketAddress leak in proxy_lookup_ready()

g_proxy_address_new() returns a new GProxyAddress, so we must unref it
when no longer needed.

This fixes:

==6481== 234 (48 direct, 186 indirect) bytes in 1 blocks are definitely lost in loss record 10,062 of 10,
==6481==    at 0x31FF230A58: g_type_create_instance (gtype.c:1849)
==6481==    by 0x31FF21501A: g_object_new_internal (gobject.c:1774)
==6481==    by 0x31FF216EB4: g_object_new_valist (gobject.c:2033)
==6481==    by 0x31FF217220: g_object_new (gobject.c:1617)
==6481==    by 0x3D4386F33A: g_proxy_address_new (gproxyaddress.c:325)
==6481==    by 0x5717440: proxy_lookup_ready (spice-session.c:2011)
==6481==    by 0x3D43885082: g_task_return_now (gtask.c:1088)
==6481==    by 0x3D438850B8: complete_in_idle_cb (gtask.c:1102)
==6481==    by 0x31FEE4A0B9: g_main_dispatch (gmain.c:3122)
==6481==    by 0x31FEE4A0B9: g_main_context_dispatch (gmain.c:3737)
==6481==    by 0x31FEE4A44F: g_main_context_iterate.isra.29 (gmain.c:3808)
==6481==    by 0x31FEE4A771: g_main_loop_run (gmain.c:4002)
==6481==    by 0x363AC06CC4: gtk_main (in /usr/lib64/libgtk-3.so.0.1600.1)

freedesktop-unofficial-mirror/spice__spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,Fantu/spice-gtk,SPICE/spice-gtk,Fantu/spice-gtk,Fantu/spice-gtk,Fantu/spice-gtk,fgouget/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,SPICE/spice-gtk,SPICE/spice-gtk,SPICE/spice-gtk,fgouget/spice-gtk,flexVDI/spice-gtk,flexVDI/spice-gtk,fgouget/spice-gtk