bug#12861: wrong default value when completing in woman-file-name

[Jonas Bernoulli <jonas@bernoul.li>]

Stefan Monnier writes:

>> Could you please change this so that the key sequence actually used to
>> invoke `minibuffer-complete' is unread instead of TAB (or just call
>> `minibuffer-complete' explicitly?).
>
> The patch below should fix your problem, but could you confirm it
> provides the intended completion behavior?

With emacs -Q it works but with my configuration it doesn't.  I think
that again me using <tab> instead of TAB to complete causes this.  I
will let you know once I have verified this.

The problem I see is that iff the selected topic is also the prefix of
other available topics (e.g. git-prune[-packed]) then pressing <tab>
when completing the *file-name* does not cause the *Completions* buffer
to appear.  When I do something before pressing <tab> (e.g. delete a
character or C-h c <tab> to verify it is indeed bound to
`minibuffer-complete') and *then* press <tab> then the completions are
shown, just not when completing immediately.

-- Jonas