hinted handoff: Segmentation fault before migration to host ID

[dawmd]

If hinted handoff is still IP-based and there is a hint directory representing an IP without a corresponding mapping to a host ID in locator::token_metadata, an attempt to initialize its endpoint manager will result in a segmentation fault.

The flawed fragment (manager::initialize_endpoint_managers):

const locator::host_id host_id = maybe_host_id_or_ep->resolve_id(*tmptr);