Fix Enchant dictionary finding routine

Fix Enchant dictionary finding routine

* lisp/textmodes/ispell.el (ispell-find-enchant-dictionaries): Don’t
  pass `buffer-string' to enchant-lsmod. Remove zero-length substrings
  from the split output of `enchant-lsmod`, as the output ends with a
  separator. Pass the current language to
  `ispell--get-extra-word-characters', so we get the result for the
  current language, not the default language. (Patch from Jorge P. de
  Morais Neto.)