pixbufmanipulator: fix crash when CM has no name

If the contactmethod doesn't have a name, we should use the id and don't
try to get the first letter.

Change-Id: I748dd89a1580e3ea7e416f50d88b2e04cfc750e0
Reviewed-by: Philippe Gorley <philippe.gorley@savoirfairelinux.com>