[iOS Reading List] Only allow offline URL when the offline file exists.

ios/chrome/browser/ui/reading_list/offline_page_native_content.mm

Index: ios/chrome/browser/ui/reading_list/offline_page_native_content.mm
diff --git a/ios/chrome/browser/ui/reading_list/offline_page_native_content.mm b/ios/chrome/browser/ui/reading_list/offline_page_native_content.mm
index 9b3a5cddc0251af85669952d866e1b3e3805a37d..cd1c109ab442f1f2590e0bfd66637be353df1869 100644
--- a/ios/chrome/browser/ui/reading_list/offline_page_native_content.mm
+++ b/ios/chrome/browser/ui/reading_list/offline_page_native_content.mm
@@ -86,6 +86,11 @@
 }
 
 - (void)reload {
+  if (!_entryURL.is_valid()) {
+    // If entryURL is not valid, the restoreOnlineURL will fail and the |reload|
+    // will be called in a loop. Early return here.
+    return;
+  }
   [self restoreOnlineURL];
   _webState->GetNavigationManager()->Reload(web::ReloadType::NORMAL,
                                             false /*check_for_repost*/);