Remove handling of fallback arguments from `PDFViewerApplication.open`

The method signature was improved in PR 6546, which was included in the `1.2.109` release from last November.
Hence I think that we should now be able to remove the fallback code for the old method signature. Note that this patch now throws an `Error` in `GENERIC` builds, to clearly indicate that the `open` callsite must be modified.

web/app.js

@@ -562,25 +562,12 @@ var PDFViewerApplication = {
    *                      is opened.
    */
   open: function pdfViewOpen(file, args) {
-    var scale = 0;
+//#if GENERIC
     if (arguments.length > 2 || typeof args === 'number') {
-      console.warn('Call of open() with obsolete signature.');
+      return Promise.reject(
-      if (typeof args === 'number') {
+        new Error('Call of open() with obsolete signature.'));
-        scale = args; // scale argument was found
-      }
-      args = arguments[4] || null;
-      if (arguments[3] && typeof arguments[3] === 'object') {
-        // The pdfDataRangeTransport argument is present.
-        args = Object.create(args);
-        args.range = arguments[3];
-      }
-      if (typeof arguments[2] === 'string') {
-        // The password argument is present.
-        args = Object.create(args);
-        args.password = arguments[2];
-      }
     }
-
+//#endif
     if (this.pdfLoadingTask) {
       // We need to destroy already opened document.
       return this.close().then(function () {
@@ -591,7 +578,7 @@ var PDFViewerApplication = {
       }.bind(this));
     }
 
-    var parameters = Object.create(null);
+    var parameters = Object.create(null), scale;
     if (typeof file === 'string') { // URL
       this.setTitleUsingUrl(file);
       parameters.url = file;
@@ -605,6 +592,13 @@ var PDFViewerApplication = {
       for (var prop in args) {
         parameters[prop] = args[prop];
       }
+
+      if (args.scale) {
+        scale = args.scale;
+      }
+      if (args.length) {
+        this.pdfDocumentProperties.setFileSize(args.length);
+      }
     }
 
     var self = this;
@@ -625,7 +619,7 @@ var PDFViewerApplication = {
     // Listen for unsupported features to trigger the fallback UI.
     loadingTask.onUnsupportedFeature = this.fallback.bind(this);
 
-    var result = loadingTask.promise.then(
+    return loadingTask.promise.then(
       function getDocumentCallback(pdfDocument) {
         self.load(pdfDocument, scale);
       },
@@ -655,11 +649,6 @@ var PDFViewerApplication = {
         throw new Error(loadingErrorMessage);
       }
     );
-
-    if (args && args.length) {
-      PDFViewerApplication.pdfDocumentProperties.setFileSize(args.length);
-    }
-    return result;
   },
 
   download: function pdfViewDownload() {