Introduce more optional chaining in the code-base

Also, use logical OR assignment a bit more.

src/core/worker_stream.js

@@ -40,9 +40,8 @@ class PDFWorkerStream {
   }
 
   cancelAllRequests(reason) {
-    if (this._fullRequestReader) {
+    this._fullRequestReader?.cancel(reason);
-      this._fullRequestReader.cancel(reason);
+
-    }
     for (const reader of this._rangeRequestReaders.slice(0)) {
       reader.cancel(reason);
     }

src/display/api.js

@@ -3153,11 +3153,7 @@ class PDFObjects {
    * @returns {Object}
    */
   #ensureObj(objId) {
-    const obj = this.#objs[objId];
+    return (this.#objs[objId] ||= {
-    if (obj) {
-      return obj;
-    }
-    return (this.#objs[objId] = {
       capability: new PromiseCapability(),
       data: null,
     });

src/pdf.sandbox.js

@@ -107,9 +107,7 @@ class Sandbox {
   }
 
   dumpMemoryUse() {
-    if (this._module) {
+    this._module?.ccall("dumpMemoryUse", null, []);
-      this._module.ccall("dumpMemoryUse", null, []);
-    }
   }
 
   nukeSandbox() {