Steps to reproduce
1. Create a course.
2. Add an image to a topic summary.
3. Add a page with an image.
Add a lesson. Add an image to a content page. (resolved in MDL-42212)
5. Add a wiki. Add an image to the first page.
6. Open the file picker from any of the added images.
All 4 images show up (in different folders) in the server files area of the file picker.
Only the images added to the topic summary and the page show up. The images added to
the lesson and the wiki are not shown – not even if the file picker is opened from inside the activity.
It might not be a very realistic scenario to reuse an image added to a lesson or wiki page, but the behaviour feels inconsistent.