fix: follow up again

Signed-off-by: yihong0618 <zouzou0208@gmail.com>

Author: yihong0618

Lib/pdb.py

@@ -1412,6 +1412,9 @@ def do_break(self, arg, temporary=False):
     # To be overridden in derived debuggers
     def defaultFile(self):
         """Produce a reasonable default."""
+        if self.curframe is None:
+            self.error("No current frame.")
+            return None
         filename = self.curframe.f_code.co_filename
         if filename == '<string>' and self.mainpyfile:
             filename = self.mainpyfile