* fix: getPageHolder would always return the first split, as they share the same index
* split pages have the same number, we need an extra check to know whether we move forward or back
(cherry picked from commit 2f07f226b8182699884262ac67139454d5b7070d)
# Conflicts:
# app/src/main/java/eu/kanade/tachiyomi/ui/reader/viewer/pager/PagerViewer.kt