JPEG compression output silently fails

[hfiguiere]

If I set the Grayscale/Colour compression to JPEG, no output gets written and I get on the console:

file: JPEG compression support is not configured.

This happens because in that context (flatpak) libtiff is build without JPEG compression. (fixing it as we speak)

The bug here is that there is no error displayed to the user, nor fallback, things just don't work.

[hfiguiere]

From a user standpoint I see two things:

• pop an error saving the file with JPEG compression and it's not available; and fall back to the default (LZW?)
• disable the option in the settings so that it can't be selected.