don't try to remove tmp folder if it's already been removed

anki/utils.py

@@ -296,6 +296,7 @@ def tmpdir():
     global _tmpdir
     if not _tmpdir:
         def cleanup():
+            if os.path.exists(_tmpdir):
                 shutil.rmtree(_tmpdir)
         import atexit
         atexit.register(cleanup)