bug#60893: 30.0.50; ad-deactive has broken interactive TAB completion

[Dima Kogan]

Hi. I'm seeing this in the bleeding-edge build of emacs from git:

1. emacs -Q

2. M-x load-library advice

3. eval:   (defadvice open-line (before dummy-advice (N) activate) 5)

   The actual advice doesn't matter. As long as something is advised
   somewhere

4. M-x ad-deactivate TAB

It should try to complete to a list of existing advised functions.
Intead it throws an error:

  completion--some: Wrong type argument: listp, "open-line"

Thanks!