fallout from 37689 and 39949, completing ~-/<tab> broken when no OLDPWD

[Mikael Magnusson <mikachu@xxxxxxxxx>]

Prior to 37689 it worked fine (completing files in the current
directory), after that commit it completed nothing, after 39949 it
started instead printing
_path_files:309: no such user or named directory: -
for each run through the completion system (so 3 times in my setup, 1
by default). Doing
 % echo ~-/
 /tmp
still works fine and prints the current directory, doing
 % a='~-/'; echo $~a
 zsh: no such user or named directory: -
exhibits the error, and that's exactly what the completer does on line
309 unsurprisingly:
  elif [[ "$linepath" = [-+] ]]; then
    realpath=${~:-\~$linepath}/


-- 
Mikael Magnusson