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
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.
When scrolling really fast, the delta value could increase, which leads to incorrect trackpad detection, because the delta value is not consistent over consecutive scroll events
In case the previous page in the history should be ignored, the back button just went back to the root page (library).
Instead, it should try to go back to the next page in the history until there is no page to go back to anymore.
A forced refresh is only necessary in case the webui was already loaded and thus, still uses outdated files from the old version.
In case the app just got freshly opened in a tab, a refresh is not necessary because the latest files are already being used.
In that case, just show an update dialog which won't force a tab refresh.
