Merge pull request #8 from uw4/patch-1

Backport: fix varargs (i.e. <n+:n>) signature validation

src/jsonata/signature.py

@@ -307,6 +307,7 @@ def validate(self, args: Any, context: Optional[Any]) -> Optional[Any]:
                             validated_args.append(arg)
                             arg_index += 1
                         else:
+                            arg = args[arg_index] if arg_index < len(args) else None
                             validated_args.append(arg)
                             arg_index += 1
             return validated_args