Plug a mem leak in get_uninitialized_connection

Plug a mem leak in get_uninitialized_connection

Free the bus address after creating the singleton.

==26308== 39,736 (10,517 direct, 29,219 indirect) bytes in 388 blocks
are definitely lost in loss record 14 of 15
==26308==    at 0x4024D2E: malloc (vg_replace_malloc.c:207)
==26308==    by 0x4079A90: g_malloc (gmem.c:135)
==26308==    by 0x4079DC8: g_malloc_n (gmem.c:252)
==26308==    by 0x4095607: g_strdup (gstrfuncs.c:102)
==26308==    by 0x4216B9A: g_dbus_address_get_for_bus_sync
(gdbusaddress.c:961)
==26308==    by 0x422A7AE: get_uninitialized_connection
(gdbusconnection.c:5241)

Bug #618622.