Revert "Exit activity directly when back-pressed"

This reverts commit e327b4e84b.

app/src/main/java/eu/kanade/tachiyomi/ui/reader/ReaderActivity.kt

@@ -639,7 +639,8 @@ class ReaderActivity : EhActivity() {
         } else {
             if (readerPreferences.fullscreen().get()) {
                 windowInsetsController.hide(WindowInsetsCompat.Type.systemBars())
-                windowInsetsController.systemBarsBehavior = WindowInsetsControllerCompat.BEHAVIOR_SHOW_BARS_BY_TOUCH
+                windowInsetsController.systemBarsBehavior =
+                    WindowInsetsControllerCompat.BEHAVIOR_SHOW_TRANSIENT_BARS_BY_SWIPE
             }
 
             if (animate) {