ObjectPicker: markDirty(AllDirty) when we change the enabled property

Otherwise we would simply change it internally but this wouldn't lead to any actual changes in how we handle pick events.

Change-Id: I71aedc74db538978a939620d053af3167fd67dc4 Reviewed-by: Sean Harmer sean.harmer@kdab.com (cherry picked from commit d32ff6b4) Reviewed-by: Qt Cherry-pick Bot cherrypick_bot@qt-project.org