fix: revert another change

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

Author: yihong0618

Lib/pdb.py

@@ -1408,10 +1408,7 @@ 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:
-            filename = '<string>'
-        else:
-            filename = self.curframe.f_code.co_filename
+        filename = self.curframe.f_code.co_filename
         if filename == '<string>' and self.mainpyfile:
             filename = self.mainpyfile
         return filename