Attach (recommended) or Link to PDF file here:
[issue13075.pdf](https://github.com/mozilla/pdf.js/files/6117265/issue13075.pdf)

Configuration:
- Web browser and its version: Node.js 14.15.5
- Operating system and its version: Mac OS 11.2.1
- PDF.js version: master/2.7.570/2.6.347/1.10.100
- Is a browser extension: false

Steps to reproduce the problem:
1. const fileBuffer = fs.readFileSync('./pdf')
2. PDFJS.getDocument(fileBuffer)
3. fileBuffer.buffer has junk data at the start and at the end. Randomly, pdfjs can not read a buffer, whose buffer.buffer contains random memory junk data in fileBuffer.buffer

What is the expected behavior? pdfjs ignores a buffer.buffer and reads only buffer

What went wrong? (add screenshot)
I've catched that random error and wrote fileBuffer.buffer of the error buffer to a file named issue13075.pdf
I've recreated a buffer that has the wrong buffer.buffer (see line 6). Pdfjs fails to read that buffer (console.log('Fail')).
The Uint8Array of that buffer, pdfjs correctly reads (console.log('OK')).
![image](https://user-images.githubusercontent.com/8398353/110660366-59f1a780-8178-11eb-94c2-29be826c2118.png)


codesandbox:
https://codesandbox.io/s/pdfjs-loading-from-buffer-issue-9h4fd?file=/src/index.js

* @property {Promise<PDFDocumentProxy>} promise - Promise for document loading
 *   task completion.
 * @property {function} destroy - Abort all network requests and destroy
 *   the worker. Returns a promise that is resolved when destruction is
 *   completed.
 */
/**
 * @type {any}
 * @ignore
 */
const PDFDocumentLoadingTask = (function PDFDocumentLoadingTaskClosure() {
  let nextDocumentId = 0;
  /**
   * The loading task controls the operations required to load a PDF document
   * (such as network requests) and provides a way to listen for completion,
   * after which individual pages can be rendered.
   */
  
  class PDFDocumentLoadingTask {
    constructor() {
      this._capability = createPromiseCapability();
      this._transport = null;
      this._worker = null;
      /**
       * Unique identifier for the document loading task.
       * @type {string}
       */
      this.docId = "d" + nextDocumentId++;
      /**
       * Whether the loading task is destroyed or not.