- Reuse isAudio and isVideo instead of re-implementing them
- In IsImage, return early is the mimetype is enough, instead of systematically
lowercasing the url as well.
- Extract the common parts of the two ProxifyAbsoluteURL implementations into a
private function, make the code smaller and clearer.
- Fix a logic error where `A && B || C` was used instead of `A && (B || C)
