Check for undefined url (#8640)

* Check for undefined

new URL(file, window.location.href) throws the following error in IE11 + iPad Safari:
Unable to get property 'replace' of undefined or null reference

* Adapting previous change to pdf.js code standards

Added curly braces

* Moved check for undefined above try/catch

web/app.js

@@ -1403,6 +1403,9 @@ if (typeof PDFJSDev === 'undefined' || PDFJSDev.test('GENERIC')) {
   const HOSTED_VIEWER_ORIGINS = ['null',
     'http://mozilla.github.io', 'https://mozilla.github.io'];
   validateFileURL = function validateFileURL(file) {
+    if (file === undefined) {
+      return;
+    }
     try {
       let viewerOrigin = new URL(window.location.href).origin || 'null';
       if (HOSTED_VIEWER_ORIGINS.indexOf(viewerOrigin) >= 0) {