Set the filename/filetype before attempting to parse (#738)

Fixes #19 by setting the file type before attempting the parse. You’ll
now be able to change the import options even if the first import
attempt failed.

<img width="826" alt="Screenshot_2023-03-10 07 40 23"
src="https://user-images.githubusercontent.com/25517624/224318498-565e1835-8820-4eaf-9e58-df33bb46d744.png">