fix segfault in got_contact_list_attributes_cb
fix segfault in got_contact_list_attributes_cb

tp_simple_client_factory_ensure_contact returns NULL for protocols, if
tp_connection_has_immortal_handles=0. Right now its happened for any
telepathy-python based protocols (butterfly, sunsine, mixer).

when tp_simple_client_factory_ensure_contact returns NULL,
tp_simple_client_factory_ensure_contact just segfault in
_tp_contact_set_attributes.

lets assume that contact sometimes NULL here, and skip them

Signed-off-by: Maksim Melnikau <8289e789c2c98de3ecfec76aa974e3365e3403b9@gmail.com>
[edited for coding style, added a comment -smcv]
Reviewed-by: Simon McVittie <2b470b34502dbf3ba4bcc04ea7e64f4e0e104f33@collabora.co.uk>

Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib