Bug 15306

When joining a chatroom gabble crash (bug #15198) and it produce an assert in tp-glib so empathy crash:

** tp-glib:ERROR:(connection.c:185):tp_connection_continue_introspection: assertion failed: (self->priv->introspect_needed != NULL)

Program received signal SIGABRT, Aborted.
[Switching to Thread 0x7f361ae187c0 (LWP 23750)]
0x00007f36154ea0e5 in raise () from /lib/libc.so.6
(gdb) bt
#0  0x00007f36154ea0e5 in raise () from /lib/libc.so.6
#1  0x00007f36154ebb40 in abort () from /lib/libc.so.6
#2  0x00007f3615d63b17 in g_assertion_message () from /usr/lib/libglib-2.0.so.0
#3  0x00007f3615d63fb2 in g_assertion_message_expr () from /usr/lib/libglib-2.0.so.0
#4  0x00007f3619c8dccd in tp_connection_continue_introspection (self=0xb2e820) at connection.c:185
#5  0x00007f3619c8dd39 in tp_connection_got_interfaces_cb (self=0xb2e820, interfaces=0x0, error=<value optimized out>, user_data=<value optimized out>, 
    user_object=<value optimized out>) at connection.c:304
#6  0x00007f3619c97f77 in _tp_cli_connection_invoke_callback_get_interfaces (self=0xb2e820, error=0x6, args=0x0, 
    generic_callback=0x7f3619c8dcd0 <tp_connection_got_interfaces_cb>, user_data=0x0, weak_object=0x0) at _gen/tp-cli-connection-body.h:778
#7  0x00007f3619cb6e3e in tp_proxy_pending_call_idle_invoke (p=<value optimized out>) at proxy.c:695
#8  0x00007f3615d41222 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#9  0x00007f3615d444d6 in ?? () from /usr/lib/libglib-2.0.so.0
#10 0x00007f3615d44797 in g_main_loop_run () from /usr/lib/libglib-2.0.so.0
#11 0x00007f3619078ee3 in gtk_main () from /usr/lib/libgtk-x11-2.0.so.0
#12 0x000000000040bdad in main (argc=1, argv=0x7fff22e582a8) at empathy.c:449