Further changes to ensure that copy-keymap doesn't segfault

Further changes to ensure that copy-keymap doesn't segfault

* src/keymap.c (copy_keymap_1, copy_keymap_set_char_table): Ensure
we don't recurse infinitely when using non-sparse keymaps, too.

This change makes this form not segfault:

(let ((map (make-keymap)))
  (define-key map " " map)
  (copy-keymap map))