hubble: avoid calling OnFlowDelivery with nil
hubble: avoid calling OnFlowDelivery with nil

Before this patch, OnFlowDelivery would be called regardless of the
event's type. Consequently, nil would be given when the event was not a
flow (e.g. a LostEvent).

Signed-off-by: Alexandre Perrin <60c6d277a8bd81de7fdde19201bf9c58a3df08f4@kaworu.ch>
Co-authored-by: Robin Hahling <042b6757f29293f4affc22596084b908e3917891@gw-computing.net>

cilium/cilium,cilium/cilium,michi-covalent/cilium,cilium/cilium,michi-covalent/cilium,cilium/cilium,michi-covalent/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium/cilium