Initialize PDFView.url = ''

The absence of this property caused the following error in PDFView.download:

   Cannot read property 'split' of undefined

This property was unset when the PDF was loaded through a typed array instead
of a URL. With the fix, the file name will default to "document.pdf", as
defined by getPDFFileNameFromURL in web/ui_utils.js

web/viewer.js

@@ -128,6 +128,7 @@ var PDFView = {
   isViewerEmbedded: (window.parent !== window),
   idleTimeout: null,
   currentPosition: null,
+  url: '',
 
   // called once when the document is loaded
   initialize: function pdfViewInitialize() {