This removes an if statement that checks if a 'page up'/'page down' event is occurring before triggering another 'page up'/'page down' event. After the recent scroll animation changes, the page scrolling animation takes long enough that Okular 'misses' 'page up'/'page down' keypresses by the user if a page scroll animation is already in progress. So, for example, pressing 'page down' quickly twice would result in Okular moving down only one page, which is confusing.
After making this change, if you quickly press
page down n times, it scrolls down n pages. Using it for a few minutes after making this change, I haven't noticed any other effects that might explain why the if statement is required.