The pjsip_host_port a_name variable was being assigned to a
temporary unnamed string that went out of scope immediately, leaving
a_name pointing to garbage.

Check return codes of calls to system

Regression introduced by commit 315e9152

Use g_strfreev on null terminated gchar **, not g_free. Otherwise you
don't free all the elements of the list.

Still crashes when creating a conference from history for conferences
created during the current session.

The wrong value was being used for "time_added" when
creating a history entry from a serialized form.