fix(addStyles): check if HTMLIFrameElement exist (#296)

Author: gregaou

lib/addStyles.js

@@ -30,7 +30,7 @@ var getElement = (function (fn) {
 		if (typeof memo[selector] === "undefined") {
 			var styleTarget = fn.call(this, selector);
 			// Special case to return head of iframe instead of iframe itself
-			if (styleTarget instanceof window.HTMLIFrameElement) {
+			if (window.HTMLIFrameElement && styleTarget instanceof window.HTMLIFrameElement) {
 				try {
 					// This will throw an exception if access to iframe is blocked
 					// due to cross-origin restrictions