Prevent useless onSelectedRangesChanged events in selectionmodels' setSelectedRanges

[evil-shrike]

Plugins slick.cellselectionmodel and slick.rowselectionmodel have function setSelectedRanges which sets selected range and fires onSelectedRangesChanged event.
Unfortunately the event is fired in any case even if range didn't change. As consequence grid fires onSelectedRowsChanged event.
That can (and does) have some useless processing.
For example slick.checkboxselectcolumn plugin in its handleSelectedRowsChanged updates column header.

    function setSelectedRanges(ranges) {
      _ranges = ranges;
      _self.onSelectedRangesChanged.notify(_ranges);
    }

I suggest to put a simple check for empty range:

    function setSelectedRanges(ranges) {
      // simle check for: empty selection didn't change, prevent firing onSelectedRangesChanged
      if ((!_ranges || _ranges.length === 0) && (!ranges || ranges.length === 0)) { return; }
      _ranges = ranges;
      _self.onSelectedRangesChanged.notify(_ranges);
    }