CJK: formatting of ‘all-on-one-line’-type entries for ‘sect2’ titles, in the generated TOC

[jfaltenbacher]

It appears that the formatting of ‘all-on-one-line’-type entries for ‘sect2’ titles, in the generated TOC,
relies only on inter-word spaces to form line break opportunities. When the entries are made up of
sect2/title/command strings, the line can protrude into the right page margin.
This may be problematic in CJK languages, where inter-word spaces are not common.

The English book has practically the same entries, but the font-size is over 1pt less, so the problem
does not present.

I have improved the presentation in the zh_CN by inserting zero-width-space characters after the
close tag in the titles.

But it is not ideal, because the page number associated with the link can appear at the beginning of
the line beneath.