the cli command `check_hold_invoice` incorrectly assumes that
`lnworker.is_accepted_mpp(payment_hash)` is true for settled invoices,
however it is not as the received mpp entries will be removed from
the `lnworker.received_mpp_htlcs` shortly after adding the preimage to
lnworker (after the htlcs got removed from the channel).
Also renames `amount_sat` in the `check_hold_invoice` response to
`amount_sat_received` to make it more obvious that this is the currently
received amount instead of the amount the invoice of `payment_hash` has
been created with.
8f9951ebed