bug#5317: Man-goto-section vs. non-existent sections

[jidanni]

   g runs the command Man-goto-section, which is an interactive compiled
   Lisp function in `man.el'.

   It is bound to g.

   (Man-goto-section)

   Query for section to move point to.

OK, but try giving it bogus sections.
*No error is told to the user.
*No C-h e or C-x ESC ESC record made of what the user tried.
*The bogus sections instead get added to *Completions*:

Possible completions are:
ACKNOWLEDGMENTS         AUTHOR  BUGS    DESCRIPTION
NAME    OPTIONS         SEE ALSO        SYNOPSIS
eeeeee  ffff    vvvv