when options)mule)set-coding-system is unselectable

[Dan Jacobson <jidanni@dman.ddts.net>]

I do find-file and notice i've found the file in the wrong coding
system.

So naturally I go to options>mule>set-coding-system and what do you
know, it's darkened, unselectible right when you need it.

OK, so maybe this is intentional.   If so at least have something that
pops up and tells the user what to do instead.

Yes, this happens in the kind of file that will produce this warning:
   "These default coding systems were tried:
      chinese-iso-8bit-unix chinese-big5
    However, none of them safely encodes the target text.

    Select one of the following safe coding systems:
      raw-text emacs-mule no-conversion" 
-- 
http://jidanni.org/ Taiwan(04)25854780