[erp5_dms] allow pdf js to return empty pdf

and fix pdf worker path

bt5/erp5_dms/SkinTemplateItem/portal_skins/erp5_dms/pdf_js/pdf.gadget.js.js

@@ -36,7 +36,9 @@
       var self = this;
       return new RSVP.Queue()
       .push(function () {
+        if (PDFViewerApplication.pdfDocument) {
           return PDFViewerApplication.pdfDocument.getData();
+        }
       })
       .push(function (data) {
         var blob = PDFJS.createBlob(data, "application/pdf");

bt5/erp5_dms/SkinTemplateItem/portal_skins/erp5_dms/pdf_js/viewer.js.js

@@ -35,7 +35,7 @@ var DISABLE_AUTO_FETCH_LOADING_BAR_TIMEOUT = 25000;
 
 function configure(PDFJS) {
   PDFJS.imageResourcesPath = './images/';
-  PDFJS.workerSrc = './pdf_js/build/pdf.worker.js';
+  PDFJS.workerSrc = './build/pdf.worker.js';
   PDFJS.cMapUrl = './web/cmaps/';
   PDFJS.cMapPacked = true;
 }