add check so that we don't try to destroy gd if it DNE

Author: etpinard

test/jasmine/assets/destroy_graph_div.js

@@ -2,5 +2,6 @@
 
 module.exports = function destroyGraphDiv() {
     var gd = document.getElementById('graph');
-    document.body.removeChild(gd);
+
+    if(gd) document.body.removeChild(gd);
 };