[build] update cdp script to generate pdls if the directory is empty

need to be able to manually update pdl files and use this script to propagate them, but reverting files does not delete the directory so need to check for empty as well

Author: titusfortner

scripts/update_cdp.py

@@ -67,7 +67,7 @@ def add_pdls(chrome_milestone):
     if os.path.isdir(old_dir):
         shutil.rmtree(old_dir)
 
-    if not os.path.isdir(target_dir):
+    if not target_dir.is_dir() or not any(target_dir.iterdir()):
         os.makedirs(target_dir, exist_ok=True)
         if os.path.isdir(source_dir):
             shutil.copytree(source_dir, target_dir, dirs_exist_ok=True)