lnwallet: consolidate redundant cases using Dual.ForParty

lnwallet/channel.go

@@ -3067,19 +3067,10 @@ func (lc *LightningChannel) fetchParent(entry *paymentDescriptor,
 
 	// The parent add height should never be zero at this point. If
 	// that's the case we probably forgot to send a new commitment.
-	case whoseCommitChain.IsRemote() &&
-		addEntry.addCommitHeights.Remote == 0:
-
+	case addEntry.addCommitHeights.GetForParty(whoseCommitChain) == 0:
 		return nil, fmt.Errorf("parent entry %d for update %d "+
-			"had zero remote add height", entry.ParentIndex,
-			entry.LogIndex)
-
-	case whoseCommitChain.IsLocal() &&
-		addEntry.addCommitHeights.Local == 0:
-
-		return nil, fmt.Errorf("parent entry %d for update %d "+
-			"had zero local add height", entry.ParentIndex,
-			entry.LogIndex)
+			"had zero %v add height", entry.ParentIndex,
+			entry.LogIndex, whoseCommitChain)
 	}
 
 	return addEntry, nil