message: multi-statement checkbox code fix 2
diff: @@ -1829,8 +1829,7 @@ UI.widgets.makeSelectForNestedCategory = function (
  ** made if the checkbox is checed and unchecked respectively.
  ** tristate: Allow ins, or del, or neither
  */
  -function buildCheckboxForm (dom, kb, lab, del, ins, form, store, tristate) {
  - if (del && del.length && del.length === 0) del = null // to fail an if
  +function buildCheckboxForm (dom, kb, lab, del, ins, form, store, tristate) { // 20190115
  var box = dom.createElement('div')
  var tx = dom.createTextNode(lab)
  var editable = UI.store.updater.editable(store.uri)
  @@ -1856,14 +1855,14 @@ function buildCheckboxForm (dom, kb, lab, del, ins, form, store, tristate) {
  ins = fix(ins)
  del = fix(del)
  - function holdsAll (kb, a) {
  + function holdsAll (a) {
  let missing = a.filter(st => !kb.holds(st.subject, st.predicate, st.object, st.why))
  return missing.length === 0
  }
  function refresh () {
  - var state = holdsAll(kb, ins)
  + var state = holdsAll(ins)
  if (del.length) {
  - var negation = holdsAll(kb, del)
  + var negation = holdsAll(del)
  if (state && negation) {
  box.appendChild(UI.widgets.errorMessageBlock(dom,
  'Inconsistent data in store!\n' + ins + ' and\n' + del))
  