Add isnan() function for IE

srcjs/output_binding_image.js

@@ -1132,7 +1132,7 @@ imageutils.createBrush = function($el, opts, coordmap, expandPixels) {
     const bounds_data = boundsData();
     // Check to see if we have valid boundsData
     for (let val in bounds_data) {
-      if (Number.isNaN(bounds_data[val])) return;
+      if (isnan(bounds_data[val])) return;
     }
 
     boundsData(bounds_data);

srcjs/utils.js

@@ -254,6 +254,12 @@ function mapValues(obj, f) {
   return newObj;
 }
 
+// This is does the same as Number.isNaN, but that function unfortunately does
+// not exist in any version of IE.
+function isnan(x) {
+  return typeof(x) === 'number' && isNaN(x);
+}
+
 // Binary equality function used by the equal function.
 function _equal(x, y) {
   if ($.type(x) === "object" && $.type(y) === "object") {