PluginDelegate: Fix bugs and regressions
Add leading item property for backward compatibility
At least Search KCM in plasma-desktop uses it to add ListItemDragHandle.
Fix eliding text
Implicit size is an arbitrary decimal value, but Layout types surprisingly round down any explicitly set preferred/min/max sizes.
Defend against null model object
Can be observed in Plasma Search KCM (a.k.a. kcm_plasmasearch) simply by scrolling the list back and forth. There the PluginDelegate component is wrapped in another item so that the delegate's ListItemDragHandle could somehow work.
Edited by ivan tkachenko