Fix a couple of crashes. First was to avoid problem caused by KIconLoader::global...

Fix a couple of crashes.  First was to avoid problem caused by KIconLoader::global()->theme() returning 0 (which according to the API, it can do).  Second was to fix the 'lastIndex' member of KCategorizedView::Private being out of date when used.  According to the comments this member existed as an optimization.  However in the only function where it is used, scrollbar updates are also performed.  This will be several orders of magnitude more expensive than the 3 constant-time operations on Qt containers (QHash,QList) which the optimization avoided.  So I removed the 'lastIndex' member and moved the calculation to where the data is needed.

svn path=/trunk/KDE/kdebase/apps/; revision=691574