Make the ObjectLoader use more efficient methods when determining if data needs to be loaded

Currently, for data in `ChunkedStream` instances, the `getMissingChunks` method is used in a couple of places to determine if data is already available or if it needs to be loaded.

When looking at how `ChunkedStream.getMissingChunks` is being used in the `ObjectLoader` you'll notice that we don't actually care about which *specific* chunks are missing, but rather only want essentially a yes/no answer to the "Is the data available?" question.
Furthermore, when looking at how `ChunkedStream.getMissingChunks` itself is implemented you'll notice that it (somewhat expectedly) always iterates over *all* chunks.

All in all, using `ChunkedStream.getMissingChunks` in the `ObjectLoader` seems like an unnecessary "heavy" and roundabout way to obtain a boolean value. However, it turns out there already exists a `ChunkedStream.allChunksLoaded` method, consisting of a *single* simple check, which seems like a perfect fit for the `ObjectLoader` use cases.
In particular, once the *entire* PDF document has been loaded (which is usually fairly quick with streaming enabled), you'd really want the `ObjectLoader` to be as simple/quick as possible (similar to e.g. loading a local files) which this patch should help with.

Note that I wouldn't expect this patch to have a huge effect on performance, but it will nonetheless save some CPU/memory resources when the `ObjectLoader` is used. (As usual this should help larger PDF documents, w.r.t. both file size and number of pages, the most.)

src/core/chunked_stream.js

@@ -285,6 +285,12 @@ class ChunkedStream {
       }
       return missingChunks;
     };
+    ChunkedStreamSubstream.prototype.allChunksLoaded = function() {
+      if (this.numChunksLoaded === this.numChunks) {
+        return true;
+      }
+      return this.getMissingChunks().length === 0;
+    };
 
     const subStream = new ChunkedStreamSubstream();
     subStream.pos = subStream.start = start;

src/core/obj.js

@@ -27,7 +27,6 @@ import { Lexer, Parser } from './parser';
 import {
   MissingDataException, toRomanNumerals, XRefEntryException, XRefParseException
 } from './core_utils';
-import { ChunkedStream } from './chunked_stream';
 import { CipherTransformFactory } from './crypto';
 import { ColorSpace } from './colorspace';
 
@@ -2072,14 +2071,14 @@ let ObjectLoader = (function() {
   }
 
   ObjectLoader.prototype = {
-    load() {
-      this.capability = createPromiseCapability();
-      // Don't walk the graph if all the data is already loaded.
-      if (!(this.xref.stream instanceof ChunkedStream) ||
-          this.xref.stream.getMissingChunks().length === 0) {
-        this.capability.resolve();
-        return this.capability.promise;
+    async load() {
+      // Don't walk the graph if all the data is already loaded; note that only
+      // `ChunkedStream` instances have a `allChunksLoaded` method.
+      if (!this.xref.stream.allChunksLoaded ||
+          this.xref.stream.allChunksLoaded()) {
+        return undefined;
       }
+      this.capability = createPromiseCapability();
 
       let { keys, dict, } = this;
       this.refSet = new RefSet();
@@ -2126,7 +2125,7 @@ let ObjectLoader = (function() {
           let foundMissingData = false;
           for (let i = 0, ii = baseStreams.length; i < ii; i++) {
             let stream = baseStreams[i];
-            if (stream.getMissingChunks && stream.getMissingChunks().length) {
+            if (stream.allChunksLoaded && !stream.allChunksLoaded()) {
               foundMissingData = true;
               pendingRequests.push({ begin: stream.start, end: stream.end, });
             }