add comment as to why test is required

Author: SWvheerden

src/ln/channel.rs

@@ -2102,7 +2102,7 @@ impl Channel {
 		if !self.pending_inbound_htlcs.is_empty() || !self.pending_outbound_htlcs.is_empty() {
 			return Err(HandleError{err: "Remote end sent us a closing_signed while there were still pending HTLCs", action: None});
 		}
-		if msg.fee_satoshis > 21000000 * 10000000 { //is this test required? We check for a much lower amount below, thus if that one will fail, this one will always fail?
+		if msg.fee_satoshis > 21000000 * 10000000 { //this is required to stop potential overflow in build_closing_transaction
 			return Err(HandleError{err: "Remote tried to send us a closing tx with > 21 million BTC fee", action: None});
 		}