`iecodebook`: `verify` option fails when there are no value labels

Returns:

```
Data signature can be found at at [path]
key variable list_name is byte in master but str1 in using data
key variable value is byte in master but str1 in using data
    Each key variable (on which observations are matched) must be of the same generic type in the master and using
    datasets.  Same generic type means both numeric or both string.
r(106);
```