tapchannel: ensure the prev witness prev ID is set for 2nd level spends

Otherwise, we'll still be pointing to the wrong asset UTXO, even though
the vIn was updated.

Author: Roasbeef

tapchannel/aux_sweeper.go

@@ -2215,6 +2215,10 @@ func (a *AuxSweeper) registerAndBroadcastSweep(req *sweep.BumpRequest,
 			for _, vIn := range vPkt.Inputs {
 				vIn.PrevID.OutPoint = sweepSet.btcInput.OutPoint()
 			}
+
+			for _, vOut := range vPkt.Outputs {
+				vOut.Asset.PrevWitnesses[0].PrevID.OutPoint = sweepSet.btcInput.OutPoint()
+			}
 		}
 	}