p-fileupload + ie9 error

[mdmota]

**I'm submitting a ...**
[x ] bug report => Search github for a similar issue or PR before submitting

Code Demo
https://stackblitz.com/edit/angular-cjkq6s

**Current behavior**
When i choose file, console show error : files is undefined . fileupload.js line 89

Code: Select all

var files = event.dataTransfer ? event.dataTransfer.files : event.target.files;
        for (var i = 0; i < files.length; i++) {	'}' esperado

**Expected behavior**
Show name of file choosed inside component p-fileupload

**Minimal reproduction of the problem with instructions**
Click 'choose' and select any file

**Please tell us about your environment:**
VS Code 1.23.1

* **Angular version:** 5.2.0

* **PrimeNG version:** 5.2.3

* **Browser:** [all | Chrome XX | Firefox XX | IE 9 | Safari XX | Mobile Chrome XX | Android X.X Web Browser | iOS XX Safari | iOS XX UIWebView | iOS XX WKWebView ]
IE9 dont work
Works in ie10+, chrome and firefox

* **Language:** [all | TypeScript 2.5.3 | ES5]

* **Node (for AoT issues):** `node --version` = 8.9.4