Fix None value check

Co-authored-by: Bartosz Sławecki <bartosz@ilikepython.com>

Author: cocolato

Lib/pdb.py

@@ -1316,7 +1316,7 @@ def do_commands(self, arg):
         """
         if not arg:
             for bp in reversed(bdb.Breakpoint.bpbynumber):
-                if not bp:
+                if bp is None:
                     continue
                 bnum = bp.number
                 break