[iOS][Cherry-pick] Fix Reading List promo corner after last item is r…

…emoved

In the Reading List, the promo cell background rounded corners becomes
right angles when the last item is removed.

Changing the separator style while the cell is shown without reloading
seems to be the cause of the issue. This CL removes the separatorStyle
change which doesn't seem to affect the UI.

Video taken after the fix:
https://drive.google.com/file/d/1eGH6UZ4NXuutkNkyMOVWgRdPj5wSsgCG/view?usp=drive_link

(cherry picked from commit b6dd374)

Bug: 1441989
Change-Id: I07c55a625316e14958f0e51b24bbf6dc8f739bd4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4556332
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Commit-Queue: Menghan Yang <myuu@google.com>
Cr-Original-Commit-Position: refs/heads/main@{#1148523}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4567944
Cr-Commit-Position: refs/branch-heads/5790@{#127}
Cr-Branched-From: 1d71a33-refs/heads/main@{#1148114}

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

@@ -226,9 +226,11 @@ - (void)viewDidLoad {
   self.dragDropHandler.dragDataSource = self;
   self.tableView.dragDelegate = self.dragDropHandler;
   self.tableView.dragInteractionEnabled = true;
+  self.tableView.separatorStyle = UITableViewCellSeparatorStyleSingleLine;
 }
 
 - (void)viewWillAppear:(BOOL)animated {
+  [super viewWillAppear:animated];
   // In case the sign-in promo visibility is changed before the first layout,
   // we need to refresh the empty view margin after the layout is done, to apply
   // the correct top margin value according to the promo view's height.
@@ -1139,7 +1141,6 @@ - (void)tableIsNotEmpty {
   [self loadItems];
   [self.audience readingListHasItems:YES];
   self.tableView.alwaysBounceVertical = YES;
-  self.tableView.separatorStyle = UITableViewCellSeparatorStyleSingleLine;
   [self removeEmptyTableView];
 }
 
@@ -1160,7 +1161,6 @@ - (void)tableIsEmpty {
   self.navigationItem.largeTitleDisplayMode =
       UINavigationItemLargeTitleDisplayModeNever;
   self.tableView.alwaysBounceVertical = NO;
-  self.tableView.separatorStyle = UITableViewCellSeparatorStyleNone;
   [self.audience readingListHasItems:NO];
   [self updateEmptyViewTopMargin];
 }