[Mac] Fix a crash in handling keyboard shortcuts for empty bookmark folder menus.

chrome/browser/ui/cocoa/bookmarks/bookmark_bar_folder_controller.mm

Index: chrome/browser/ui/cocoa/bookmarks/bookmark_bar_folder_controller.mm
diff --git a/chrome/browser/ui/cocoa/bookmarks/bookmark_bar_folder_controller.mm b/chrome/browser/ui/cocoa/bookmarks/bookmark_bar_folder_controller.mm
index 6f411fa3e9b6b3709954508f6e3878805a07e685..35935cc3665ff810dbf8342c4dca7790bc59c9b5 100644
--- a/chrome/browser/ui/cocoa/bookmarks/bookmark_bar_folder_controller.mm
+++ b/chrome/browser/ui/cocoa/bookmarks/bookmark_bar_folder_controller.mm
@@ -1635,6 +1635,9 @@ static BOOL ValueInRangeInclusive(CGFloat low, CGFloat value, CGFloat high) {
   if (index == selectedIndex_)
     return;
 
+  if (index >= 0 && [[buttons_ objectAtIndex:index] isEmpty])
+    index = -1;
+
   [self setStateOfButtonByIndex:selectedIndex_ state:NO];
   [self setStateOfButtonByIndex:index state:YES];
   selectedIndex_ = index;