the way we use PSBTs to sign things requires that we have the
scriptpubkey available on the utxo so we can populate the witness-utxo
field with it.
this causes problems if we don't already have the scriptpubkey cached in
the database, as in *some* cases we require a round trip to the HSM to
populate them
to get over this hump, we backfill any and all missing scriptpubkey
information for the utxo's that we hold in our wallet.
this will allow us to clean up the NULL handling of missing
scriptpubkeys.
We erase peer data after the last channel close transaction for that
peer is 100 blocks deep. We were failing to finish the migration because
the peer_id lookup on these was failing.
Now we ignore any channel with a null peer_id.
Fixes#3768
We use a database snapshot with 3 channels -- two of which have HTLCs
dangling and one is an initial open channel tx in the 'old' tx hex
format in last_tx and confirm that they are successfully updated to PSBT
format on start.
