[14.0] [FIX] attachment_preview: fix get_binary_extension

[renda-dev]

Without this fix, opening a ir.ui.menu record from the "Technical" menu with an empty icon, would raise an error.

Also added a couple of test lines that would fail without this.

Fixed pre-commit in https://github.com/OCA/knowledge/pull/462

[OCA-git-bot]

This PR has the approved label and has been created more than 5 days ago. It should therefore be ready to merge by a maintainer (or a PSC member if the concerned addon has no declared maintainer). 🤖

[aleuffre]

@OCA/document-maintainers pretty small fix, could I ask for a merge?

[pedrobaeza]

/ocabot merge patch

[OCA-git-bot]

What a great day to merge this nice PR. Let's do it! Prepared branch 14.0-ocabot-merge-pr-461-by-pedrobaeza-bump-patch, awaiting test results.

[OCA-git-bot]

@pedrobaeza The merge process could not be finalized, because command git push origin 14.0-ocabot-merge-pr-461-by-pedrobaeza-bump-patch:14.0 failed with output:

To https://github.com/OCA/knowledge
 ! [remote rejected]   14.0-ocabot-merge-pr-461-by-pedrobaeza-bump-patch -> 14.0 (cannot lock ref 'refs/heads/14.0': is at 7bd8c295fa839075ccbb0b36e29b78071daa6002 but expected 1d2b0203a7e89dede553cc6b9229ba8326b3bb34)
error: failed to push some refs to 'https://***@github.com/OCA/knowledge'

[OCA-git-bot]

Congratulations, your PR was merged at 7bd8c295fa839075ccbb0b36e29b78071daa6002. Thanks a lot for contributing to OCA. ❤️

[aleuffre]

Not sure about the error message, but the merge seems to have succeeded anyway.

Thank you!