【fix】【BOTA】当书签列表为空时，点击more，删除所有书签应该要置灰

PDF Office/PDF Master/Class/PDFWindowController/Side/LeftSide/BookMarks/KMBookMarkViewController.swift

@@ -661,6 +661,9 @@ extension KMBookMarkViewController: NSMenuDelegate, NSMenuItemValidation {
             let row = self.bookTableView.selectedRow
             return row >= 0 && row < self.dataSource.count
         }
+        if action == #selector(removeAllBookmark) {
+            return self.dataSource.count > 0
+        }
         return true
     }
 }