[Epoch Sync] Proof application should double check that the header_head is at genesis

[robin-near]

Description

When we receive an epoch sync proof, we should double check that we're applying on top of a state where header_head is at genesis. Otherwise, if we have a bug such as #12564 , we would be applying an epoch sync proof on top of an invalid state and it results in a store that has redundant data that is never cleaned up.