pyln.proto: fix receiving unknown fields in TLVs.

We can still convert these (e.g. k=1) to Python, by just using hex strings.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

contrib/pyln-proto/pyln/proto/message/message.py

@@ -521,8 +521,12 @@ def val_to_py(self, val: Dict[str, Any], otherfields: Dict[str, Any]) -> Dict[st
         ret: Dict[str, Any] = {}
         for k, v in val.items():
             field = self.find_field(k)
-            assert field
-            ret[k] = field.val_to_py(v, val)
+            if field:
+                ret[k] = field.val_to_py(v, val)
+            else:
+                # Unknown TLV, index by number.
+                assert isinstance(k, int)
+                ret[k] = v.hex()
         return ret
 
     def write(self, io_out: BufferedIOBase, v: Optional[Dict[str, Any]], otherfields: Dict[str, Any]) -> None: