[Patch] To filebuf::underflow vs codecvt::in

[Benjamin Kosnik]

> this issue has been reported to the Novell Bugzilla: the fix seems easy, 
> just don't call codecvt::in when eof is reached and there are no chars 
> to convert. Apparently this kind of behavior can be seen also in other 
> implementations. Tested x86-linux, will wait till the endo of today 
> before committing to mainline.

Thanks for this.

Looks good to me!

-benjamin