If there's a Word style reference file set but it doesn't exist, the process fails

[rikchilvers]

To replicate:

1. Set a Word style reference file. Check the process completes as expected.
2. Move/delete the reference file. Observe that the app reports a successful conversion but the expected file does not appear.

This caught me out today. Otherwise, this little app is 👌🏻 Thanks for building it!