Contacts: Ignore device null account.

As of commit 2cb5e075 which adds device contact,
the behavior is correct if there is a google account already setup, otherwise
there are two device contacts shown. So, always ignore null account.

Change-Id: I9f18a45efcaa93b8583013beb5995bf85ae58dcd
Signed-off-by: Toha <tohenk@yahoo.com>