This caused the reader to "jump to random pages" because it caused the image to get unrendered and rendered again, leading to layout shifts.
This issue existed already for a long time but could only rarely be observed because of the hacky "cache check" logic.
The changes from 9ed05f3fc0 caused this issue to be consistent in case the new service worker could not get installed due to not meeting the required installation prerequisites. If that was the case, the cache check always returned false causing the above-described behavior.
fixes#929
The server is not requesting these images through an extension; thus, it is not a problem to send them directly to the server since there is no problem of getting the server "stuck" due to extension rate limits.
Improves the image request logic by making it possible to check if an image is cached.
In case an image is cached, it does not need to be put into the image queue because it won't be sent to the server.
