Fix underline gaps in space characters

It turns out that trailing spaces are significant, e.g. when the current rendition is set to underline. Gaps where appearing in underlined text with spaces. To test, launch konsole with -p BidiRenderingEnabled=false, and run:

printf '\e[4mtest under line foo ññññ ááá ééé '

which should show no gaps in underlining, and exercises both instances of the "group non-wide characters with following spaces" code.