Fixes a regression introduced in 77411390.

Reported by Ludovic Courtès <ludo@gnu.org>.

Not all emacs packages have "...-autoloads.el" files, so there is a
chance that "~/.guix-profile/share/emacs/site-lisp" will not be added to
'load-path', so add it unconditionally.

* emacs/guix-init.el: Add guix emacs directory to 'load-path'.  Move
  requiring 'guix-emacs' to the top-level.