[Firefox regression] Fix disableRange=true bug in `PDFDataTransport…

…Stream`

Currently if trying to set `disableRange=true` in the built-in PDF Viewer in Firefox, either through `about:config` or via the URL hash, the PDF document will never load. It appears that this has been broken for a couple of years, without anyone noticing.

Obviously it's not a good idea to set `disableRange=true`, however it seems that this bug affects the PDF Viewer in Firefox even with default settings:
 - In the case where `initialData` already contains the *entire* file, we're forced to dispatch a range request to re-fetch already available data just so that file loading may complete.
 - In the case where the data arrives, via streaming, before being specifically requested through `requestDataRange`, we're also forced to re-fetch data unnecessarily.

In both cases outlined above, we're having to re-fetch already available data thus potentially delaying loading/rendering of PDF files in Firefox (and wasting resources in the process).

src/display/transport_stream.js

@@ -126,6 +126,16 @@ var PDFDataTransportStream = (function PDFDataTransportStreamClosure() {
     stream._fullRequestReader = this;
 
     this.onProgress = null; // not used
+
+    let loaded = 0;
+    for (const chunk of this._queuedChunks) {
+      loaded += chunk.byteLength;
+    }
+    this._loaded = loaded;
+
+    if (this._loaded >= this.contentLength) {
+      this._done = true;
+    }
   }
   PDFDataTransportStreamReader.prototype = {
     _enqueue: function PDFDataTransportStreamReader_enqueue(chunk) {
@@ -135,9 +145,14 @@ var PDFDataTransportStream = (function PDFDataTransportStreamClosure() {
       if (this._requests.length > 0) {
         var requestCapability = this._requests.shift();
         requestCapability.resolve({ value: chunk, done: false, });
-        return;
+      } else {
+        this._queuedChunks.push(chunk);
+      }
+      this._loaded += chunk.byteLength;
+
+      if (this._loaded >= this.contentLength) {
+        this._done = true;
       }
-      this._queuedChunks.push(chunk);
     },
 
     get headersReady() {

test/unit/api_spec.js

@@ -1526,5 +1526,28 @@ describe('api', function() {
         });
       }).catch(done.fail);
     });
+
+    it('should fetch document info and page, without range, ' +
+       'using complete initialData', function(done) {
+      let fetches = 0, loadingTask;
+
+      dataPromise.then(function(data) {
+        const transport = new PDFDataRangeTransport(data.length, data);
+        transport.requestDataRange = function(begin, end) {
+          fetches++;
+        };
+        loadingTask = getDocument({ disableRange: true, range: transport, });
+        return loadingTask.promise;
+      }).then(function(pdfDocument) {
+        expect(pdfDocument.numPages).toEqual(14);
+
+        return pdfDocument.getPage(10);
+      }).then(function(pdfPage) {
+        expect(pdfPage.rotate).toEqual(0);
+        expect(fetches).toEqual(0);
+
+        loadingTask.destroy().then(done);
+      }).catch(done.fail);
+    });
   });
 });