Fix forget page when the screen is rotated (#1674)

(cherry picked from commit e2fcfcc7a8)

app/src/main/kotlin/org/koitharu/kotatsu/reader/ui/pager/BaseReaderFragment.kt

@@ -25,11 +25,26 @@ abstract class BaseReaderFragment<B : ViewBinding> : BaseFragment<B>(), ZoomCont
 		readerAdapter = onCreateAdapter()
 
 		viewModel.content.observe(viewLifecycleOwner) {
-			if (it.state == null && it.pages.isNotEmpty() && readerAdapter?.hasItems != true) {
+			// Determine which state to use for restoring position:
-				onPagesChanged(it.pages, viewModel.getCurrentState())
+			// - content.state: explicitly set state (e.g., after mode switch or chapter change)
-			} else {
+			// - getCurrentState(): current reading position saved in SavedStateHandle
-				onPagesChanged(it.pages, it.state)
+			val currentState = viewModel.getCurrentState()
+			val pendingState = when {
+				// If content.state is null and we have pages, use getCurrentState
+				it.state == null
+					&& it.pages.isNotEmpty()
+					&& readerAdapter?.hasItems != true -> currentState
+
+				// use currentState only if it matches the current pages (to avoid the error message)
+				readerAdapter?.hasItems != true
+					&& it.state != currentState
+					&& currentState != null
+					&& it.pages.any { page -> page.chapterId == currentState.chapterId } -> currentState
+
+				// Otherwise, use content.state (normal flow, mode switch, chapter change)
+				else -> it.state
 			}
+			onPagesChanged(it.pages, pendingState)
 		}
 	}