Fix - properly add interactive resize elements

One have to use selectChild, otherwise random sub-sub childs elements
can be selected

Author: linev

modules/gpad/TFramePainter.mjs

@@ -47,7 +47,7 @@ function addDragHandler(_painter, arg) {
    function makeResizeElements(group, handler) {
       function addElement(cursor, d) {
          let clname = 'js_' + cursor.replace(/[-]/g, '_'),
-             elem = group.select('.' + clname);
+             elem = group.selectChild('.' + clname);
          if (elem.empty()) elem = group.append('path').classed(clname, true);
          elem.style('opacity', 0).style('cursor', cursor).attr('d', d);
          if (handler) elem.call(handler);