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

callback,
      params,
      objs,
      commonObjs,
      operatorList,
      pageIndex,
      canvasFactory,
      webGLContext,
      useRequestAnimationFrame = false,
      pdfBug = false,
    }) {
      this.callback = callback;
      this.params = params;
      this.objs = objs;
      this.commonObjs = commonObjs;
      this.operatorListIdx = null;
      this.operatorList = operatorList;
      this._pageIndex = pageIndex;
      this.canvasFactory = canvasFactory;
      this.webGLContext = webGLContext;
      this._pdfBug = pdfBug;
      this.running = false;
      this.graphicsReadyCallback = null;
      this.graphicsReady = false;
      this._useRequestAnimationFrame =
        useRequestAnimationFrame === true && typeof window !== "undefined";
      this.cancelled = false;
      this.capability = createPromiseCapability();
      this.task = new RenderTask(this);