missing safety checks on shift-ctrl selection on listbox

    zk.afterLoad("zul.sel, zkmax", function () {
        var _xListbox = {};
        zk.override(zul.sel.Listbox.prototype, _xListbox, {
            _focus: function (row) {
                this.shiftAnchor = null;
                return _xListbox._focus.apply(this, arguments);
            },
            _selectOne: function (row, skipFocus) {
                this.shiftAnchor = null;
                return _xListbox._selectOne.apply(this, arguments);
            },
            _toggleSelect: function (row, toSel, evt, skipFocus) {
                this.shiftAnchor = null;
                return _xListbox._toggleSelect.apply(this, arguments);
            },
            _selectUpto: function (row, evt, skipFocus) {
                /* don't touch behavior for rod listbox */
                if (this._listbox$rod) {
                    return _xListbox._selectUpto.apply(this, arguments);
                }

                var shiftAnchor = this.shiftAnchor
                        || this._focusItem
                        || ((this._lastSelectedItem && this._lastSelectedItem.parent) ?
                             this._lastSelectedItem : this.firstItem);

                this._unsetSelectAllExcept();
                this._changeSelect(shiftAnchor, true);

                if (row.isSelected()) {
                    if (!skipFocus)
                        this._focus(row);
                    return;
                }

                var focusfound = false, rowfound = false,
                    lastSelected = shiftAnchor;

                if (!lastSelected.isSelected()) {
                    var rowIndex = this.indexOfItem(row),
                        min = Number.MAX_VALUE,
                        closestSelItem;
                    for (var i = 0; i < this._selItems.length; ++i) {
                        var item = this._selItems[i],
                            index = this.indexOfItem(item),
                            diff = rowIndex - index,
                            oldmin = min;
                        if ((diff <= 0) && closestSelItem)
                            break;
                        min = Math.min(diff, min);
                        if (min != oldmin)
                            lastSelected = item;
                    }
                }
                for (var it = this.getBodyWidgetIterator(), si = this.getSelectedItem(), w; (w = it.next());) {
                    if (w.isDisabled() || !w.isSelectable()) continue;
                    if (focusfound) {
                        this._changeSelect(w, true);
                        if (w == row)
                            break;
                    } else if (rowfound) {
                        this._changeSelect(w, true);
                        if (this._isFocus(w) || w == lastSelected)
                            break;
                    } else if (!si) {
                        if (w != row)
                            continue;
                        this._changeSelect(w, true);
                        break;
                    } else {
                        rowfound = w == row;
                        focusfound = this._isFocus(w) || w == lastSelected;
                        if (rowfound || focusfound) {
                            this._changeSelect(w, true);
                            if (rowfound && focusfound)
                                break;
                        }
                    }
                }

                if (!skipFocus)
                    this._focus(row);

                this.shiftAnchor = shiftAnchor;

                this.fireOnSelect(row, evt);
            },
            onChildRemoved_: function (child) {
                if(this.shiftAnchor === child) {
                    this.shiftAnchor = null;
                }
                return _xListbox.onChildRemoved_.apply(this, arguments);
            }
         });
    });