Unify method return values in the ObjectLoader class

Given that all the methods are already asynchronous we can just use `await` more throughout this code, rather than having to explicitly return function-calls and `undefined`.
Note also how none of the `ObjectLoader.prototype.load` call-sites use the return value.

src/core/object_loader.js

@@ -54,17 +54,18 @@ function addChildren(node, nodesToVisit) {
  * entire PDF document object graph to be traversed.
  */
 class ObjectLoader {
+  refSet = null;
+
   constructor(dict, keys, xref) {
     this.dict = dict;
     this.keys = keys;
     this.xref = xref;
-    this.refSet = null;
   }
 
   async load() {
     // Don't walk the graph if all the data is already loaded.
     if (this.xref.stream.isDataLoaded) {
-      return undefined;
+      return;
     }
 
     const { keys, dict } = this;
@@ -78,10 +79,12 @@ class ObjectLoader {
         nodesToVisit.push(rawValue);
       }
     }
-    return this._walk(nodesToVisit);
+    await this.#walk(nodesToVisit);
+
+    this.refSet = null; // Everything is loaded, clear the cache.
   }
 
-  async _walk(nodesToVisit) {
+  async #walk(nodesToVisit) {
     const nodesToRevisit = [];
     const pendingRequests = [];
     // DFS walk of the object graph.
@@ -99,11 +102,10 @@ class ObjectLoader {
           currentNode = this.xref.fetch(currentNode);
         } catch (ex) {
           if (!(ex instanceof MissingDataException)) {
-            warn(`ObjectLoader._walk - requesting all data: "${ex}".`);
-            this.refSet = null;
+            warn(`ObjectLoader.#walk - requesting all data: "${ex}".`);
 
-            const { manager } = this.xref.stream;
-            return manager.requestAllChunks();
+            await this.xref.stream.manager.requestAllChunks();
+            return;
           }
           nodesToRevisit.push(currentNode);
           pendingRequests.push({ begin: ex.begin, end: ex.end });
@@ -139,11 +141,8 @@ class ObjectLoader {
           this.refSet.remove(node);
         }
       }
-      return this._walk(nodesToRevisit);
+      await this.#walk(nodesToRevisit);
     }
-    // Everything is loaded.
-    this.refSet = null;
-    return undefined;
   }
 }