fix Simplify prev txout existence check

Author: optout21

lightning/src/ln/interactivetxs.rs

@@ -1910,13 +1910,14 @@ pub(super) fn calculate_change_output_value(
 		if txin.previous_output.txid != txid {
 			return Err(AbortReason::PrevTxOutInvalid);
 		}
-		if let Some(output) = tx.as_transaction().output.get(txin.previous_output.vout as usize) {
-			total_input_satoshis = total_input_satoshis.saturating_add(output.value.to_sat());
-			let weight = estimate_input_weight(output).to_wu();
-			our_funding_inputs_weight = our_funding_inputs_weight.saturating_add(weight);
-		} else {
-			return Err(AbortReason::PrevTxOutInvalid);
-		}
+		let output = tx
+			.as_transaction()
+			.output
+			.get(txin.previous_output.vout as usize)
+			.ok_or(AbortReason::PrevTxOutInvalid)?;
+		total_input_satoshis = total_input_satoshis.saturating_add(output.value.to_sat());
+		let weight = estimate_input_weight(output).to_wu();
+		our_funding_inputs_weight = our_funding_inputs_weight.saturating_add(weight);
 	}
 	// If there is a shared input, account for it,
 	// and for the initiator also consider the fee