The previous/next chapter only ever preloaded the first page, ignoring available preload contingent.
I.e., if all leading/trailing pages of the current chapter were loaded, the reader did not keep preloading the previous/next chapters pages
The safe area inset wasn't applied everywhere, which potentially caused the scrollbar to appear while the pages should be fitting the screen
fixes#1102
In continuous reading modes the pages are always rendered regardless of if they are visible or not. This is the case to prevent layout shifts when prepending pages while scrolling up.
However, this means that a pages "load priority" and its "should load" flag changes everytime the current page changes, which causes unnecessary rerenders.
The "load priority" and "should load" flag do not matter once a page has been loaded and therefore should stay consistent once loaded.
