Fix RL crash when modifyed in background scene.

If the RL view is in background scene when the model is modified,
reloadData is called, and the number of items is updated, but rendering
is postponed until the screen is displayed.
If the model is modified again before that, it is possible that the
view access items that have been deleted since.

Bug: 1097027
Change-Id: Ibbd4d19700cf86bfda9db4ddb4d2285203f5ce0b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2428966Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Olivier Robin <olivierrobin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811200}

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

@@ -975,6 +975,12 @@ ReadingListSelectionState GetSelectionStateForSelectedCounts(
 
 // Called when the table is empty.
 - (void)tableIsEmpty {
+  // It is necessary to reloadData now, before modifying the view which will
+  // force a layout.
+  // If the window is not displayed (e.g. in an inactive scene) the number of
+  // elements may be outdated and the layout triggered by this function will
+  // generate access non-existing items.
+  [self.tableView reloadData];
   if (base::FeatureList::IsEnabled(kIllustratedEmptyStates)) {
     UIImage* emptyImage = [UIImage imageNamed:@"reading_list_empty"];
     NSString* title =