lnwallet/channel: return error in case of htlc index mismatch
lnwallet/channel: return error in case of htlc index mismatch

This commit make us return an error in case a restored HTLC from a
pending remote commit has an index that is different from our local
update log index. It is appended with the assumption that these indexes
are the same, and if they are not we cannot really continue.

aakselrod/lnd,LightningNetwork/lnd,aakselrod/lnd,LightningNetwork/lnd