lnutil.PaymentAttemptLog: fix error formatting

fixes #6249

electrum/lnonion.py

@@ -405,6 +405,11 @@ class OnionRoutingFailureMessage:
         failure_data = failure_msg[2:]
         return OnionRoutingFailureMessage(failure_code, failure_data)
 
+    def code_name(self) -> str:
+        if isinstance(self.code, OnionFailureCode):
+            return str(self.code.name)
+        return f"Unknown error ({self.code!r})"
+
 
 def construct_onion_error(reason: OnionRoutingFailureMessage,
                           onion_packet: OnionPacket,

electrum/lnutil.py

@@ -269,8 +269,12 @@ class PaymentAttemptLog(NamedTuple):
                 sender_idx = self.failure_details.sender_idx
                 failure_msg = self.failure_details.failure_msg
                 if sender_idx is not None:
-                    short_channel_id = route[sender_idx+1].short_channel_id
-                message = str(failure_msg.code.name)
+                    try:
+                        short_channel_id = route[sender_idx + 1].short_channel_id
+                    except IndexError:
+                        # payment destination reported error
+                        short_channel_id = _("Destination node")
+                message = failure_msg.code_name()
             else:
                 short_channel_id = route[-1].short_channel_id
                 message = _('Success')