Fix HTLC tx balance calculation on local commitment transactions

Fix HTLC tx balance calculation on local commitment transactions

When handling the broadcast of a local commitment transactions
(with associated CSV delays prior to spendability), we incorrectly
handled the CSV delays on HTLC transactions. This caused us to miss
spendable outputs for HTLCs which were awaiting a CSV delay.

Further, because of this, we could hit an assertion as
`get_claimable_balances` asserted that HTLCs were resolved after
the funding spend was resolved, which was not true if the HTLC did
not have a CSV delay attached (due to the above bug or due to it
being an HTLC claim by our counterparty).

This fixes both bugs, also converting some assertions to
`debug_assert`s to avoid future issues as balance mis-calculation
is not currently an indication of potential funds loss.

Thanks to Cash App for reporting this bug.