Don't assert when accessing this too early.
Sort the tool model on the server side.

While this is a useful optimization, it hardly matters for the small tool
model. This is mainly a workaround for the yet not fully understood
regression due to qtbase change bec1854cc023fb705319c582a636d5f484adafcc
that messes up our remote selection handling.
Integrate upstream fixes for KLinkItemSelectionModel.