[custom channels]: Assert fix for duplicate script key issues in MPP payments#908

guggero merged 2 commits intoupdate-to-lnd-18-4lightninglabs/lightning-terminal:update-to-lnd-18-4from

fix-htlc-mpp-duplicate-script-keylightninglabs/lightning-terminal:fix-htlc-mpp-duplicate-script-keyCopy head branch name to clipboard