#92 Assertion after trying to send to a defunct socket

[Mikhail Zabaluev]

Sometimes shutting down the stack when the network connection is brought down results in a failed assertion.
Here are the relevant debug log messages:

telepathy-sofiasip[1405]: GLIB DEBUG default - priv_r_shutdown: nua_shutdown: 100 Shutdown started

[the network connection is shut down...]

telepathy-sofiasip[1405]: tport_vsend(0x44f80): Invalid argument with (s=5 udp/213.192.59.75:5060)
telepathy-sofiasip: nua_stack.c:1874: nua_client_bind: Assertion `!nua_client_is_queued(du->du_cr)' failed.