bash-5.0-beta2 breaks ``complete -D''

[Clark Wang]

Hi Chet,

Just tried 5.0-beta2 and it broke my completion rules. It can be reproduced
with the following steps:

# complete -r
# foo() { true; }
# complete -o default -o bashdefault -D -F foo
# cd /<TAB><TAB>    <-- Here it does not list dirs under `/'. Works fine
with 4.4.

Please take a look.

-clark