[declarative] Return 0 unread messages if channel is null
[declarative] Return 0 unread messages if channel is null

Reviewed-by: Alexandr Akulich <ad71d6ef874ccc09e1a69fe0dd6443b72073e71a@gmail.com>

KDE/ktp-common-internals,KDE/ktp-common-internals,KDE/ktp-common-internals