Fix #4097: error when View invalidated immediately

Bug introduced in 28c760e

packages/blaze/view.js

@@ -354,7 +354,9 @@ Blaze._materializeView = function (view, parentView, _workStack, _intoArray) {
       // helpers in the DOM tree to be replaced might be scheduled
       // to re-run before we have a chance to stop them.
       Tracker.onInvalidate(function () {
-        domrange.destroyMembers();
+        if (domrange) {
+          domrange.destroyMembers();
+        }
       });
     }, undefined, 'materialize');
 

packages/spacebars-tests/template_tests.html

@@ -32,6 +32,10 @@
   {{/if}}
 </template>
 
+<template name="spacebars_template_test_bracketed_foo">
+  [{{foo}}]
+</template>
+
 <!-- -->
 
 

packages/spacebars-tests/template_tests.js

@@ -2749,6 +2749,30 @@ Tinytest.add('spacebars-tests - template_tests - current view in event handler',
 });
 
 
+Tinytest.add('spacebars-tests - template_tests - helper invalidates self', function (test) {
+  var tmpl = Template.spacebars_template_test_bracketed_foo;
+
+  var count = new ReactiveVar(0);
+
+  tmpl.helpers({
+    // It's unusual for a helper to have side effects, but it's possible
+    // and people do it.  Regression test for #4097.
+    foo: function () {
+      // Make count odd and return it.
+      var c = count.get();
+      if ((c % 2) === 0) {
+        count.set(c+1);
+      }
+      return c;
+    }
+  });
+
+  var div = renderToDiv(tmpl);
+  divRendersTo(test, div, '[1]');
+  count.set(2);
+  divRendersTo(test, div, '[3]');
+});
+
 Tinytest.add(
   "spacebars-tests - template_tests - textarea attrs", function (test) {
     var tmplNoContents = {