Thumbnails don't work with SVG

[matrixbot]

This issue was originally created by @Dreamsorcerer at matrix-org/dendrite#3369.

Background information

• Dendrite version or git SHA: 0.13.7
• SQLite3 or Postgres?: Postgres
• Running in Docker?: No
• go version: 1.21
• Client used (if applicable): Element Web

Description

• What is the problem: Uploaded an SVG as a Spaces icon. No icon appears in UI.
• How is this bug manifesting: Error log says "Failed to read src file" MediaID=3e59ec584581583cdc99db373f07ced46aeadb9bc0388b6abd16fdfaa439cf2a error="image: unknown format" req.id=KzRl2SSkLDWT req.method=GET req.path=/_matrix/media/v3/thumbnail/.../3e59ec584581583cdc99db373f07ced46aeadb9bc0388b6abd16fdfaa439cf2a src=/var/www/matrix/media_store/w/Y/F5VC6SeTYdF4PdcmE21ih6xLVVu7Q4LJx0HvqrzGE/file

Steps to reproduce

• Upload icon for space: https://upload.wikimedia.org/wikipedia/en/4/43/Feed-icon.svg
• View that no icon appears in sidebar, spaces page or in settings for spaces page.

[matrixbot]

This comment was originally posted by @Dreamsorcerer at matrix-org/dendrite#3369 (comment).

Isn't this also a flaw in the client or spec? If the image is an SVG, then it shouldn't be making multiple requests for different thumbnails, it should just display the original image.