[PATCH] Fix crashes on invalid input in IBM gconv modules [BZ #17325]

[Roland McGrath]

> I would like to do this in a future cleanup across all gconv modules, 
> after the 2.20 release.  For this patch, I went with the existing style 
> in the changed files.  This also simplifies backporting.

That's certainly fine.  If you noticed a thing like that when doing the
change, it's a good idea to mention explicitly in the posting what future
cleanups you intend to do.  Without that, people like me are liable to
simply review each line you touched generically for how it should look in
the end.