Use KStringHandler::preProcessWrap() when calculating the width of a

Use KStringHandler::preProcessWrap() when calculating the width of a
file name in DolphinFileItemDelegate. This makes sure that zero width
spaces (which prevent kerning) are added at the same places where
KFileItemDelegate adds them when actually rendering the name. Fixes
the problem that file names are elided and partly replaced by "..."
even though there is enough space for the full name.

CCBUG: 251121

svn path=/trunk/KDE/kdebase/apps/; revision=1179568