PendingObjectGrid: fix display of deletion of multikey fields

PendingObjectGrid: fix display of deletion of multikey fields

we did only check if the first field of a mulitfield key is being deleted,
resulting in showing no pending change at all when deleting any other,
and as long as only deletions were taking place

also when deleting the 'main' key of a multikey field, we
showed the deletion of the whole line, even when already showing
a different pending line

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>