QStandardItem::appendRow does not update model recursively

See sample `main.cpp` below for more details.

If a tree model is laid out as follows:

topItem
-> midItem
 -> bottomItem,

then after removing midItem and inserting it back as a child of topItem, `bottomItem ->model()` returns `nullptr` even though `bottomItem` is now in the model (as a child of `midItem`).