Fix linearization error messages

Since (valid) linearization data shouldn't be necessary to load and render a PDF file, I've changed two instances of `error` to `info` so that we can avoid displaying unnecessary warnings and triggering the fallback bar.

Given that files with invalid linearization dictionaries (e.g. the PDF in #4143) already displays fine, I don't think that we need to throw errors. *I hope this assumption in correct!*

Fixes #4143.