[ios] Fixed GetIndexForOffset for pending transient items.

ios/web/navigation/navigation_manager_impl.mm

Index: ios/web/navigation/navigation_manager_impl.mm
diff --git a/ios/web/navigation/navigation_manager_impl.mm b/ios/web/navigation/navigation_manager_impl.mm
index e86102b314481a4d5bb6dfed6b60922e1377a89f..76c725a58af237405744da86159b7e5860c8fa17 100644
--- a/ios/web/navigation/navigation_manager_impl.mm
+++ b/ios/web/navigation/navigation_manager_impl.mm
@@ -344,9 +344,10 @@ int NavigationManagerImpl::GetIndexForOffset(int offset) const {
                    : static_cast<int>([session_controller_ pendingEntryIndex]);
 
   if (offset < 0) {
-    if (GetTransientItem()) {
-      // Going back from transient item is a matter of discarding it and there
-      // is no need to move navigation index back.
+    if (GetTransientItem() && [session_controller_ pendingEntryIndex] == -1) {
+      // Going back from transient item that added to the end navigation stack
+      // is a matter of discarding it as there is no need to move navigation
+      // index back.
       offset++;
     }