LND #2765 changes how the LN node responds to channel breaches (attempted theft). Previously, if an attempted breach was detected, the node created a breach remedy transaction to collect all funds associated with that channel. However, when users start using watchtowers, the watchtower may create a breach remedy transaction but not include all the possible funds. (This doesn’t mean the watchtower is malicious: your node may simply not have had a chance to tell the watchtower about the latest commitments it accepted.) This PR updates the logic used to generate the breach remedy transaction so that it only collects the funds that haven’t been collected by prior breach remedy transactions, allowing recovery of any funds the watchtower didn’t collect.