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

*   before viewport transform.
 * @property {Object} [imageLayer] - An object that has `beginLayout`,
 *   `endLayout` and `appendImage` functions.
 * @property {Object} [canvasFactory] - The factory instance that will be used
 *   when creating canvases. The default value is {new DOMCanvasFactory()}.
 * @property {Object | string} [background] - Background to use for the canvas.
 *   Any valid `canvas.fillStyle` can be used: a `DOMString` parsed as CSS
 *   <color> value, a `CanvasGradient` object (a linear or radial gradient) or
 *   a `CanvasPattern` object (a repetitive image). The default value is
 *   'rgb(255,255,255)'.
 * @property {AnnotationStorage} [annotationStorage] - Storage for annotation
 *   data in forms.
 * @property {Promise<OptionalContentConfig>} [optionalContentConfigPromise] -
 *   A promise that should resolve with an {@link OptionalContentConfig}
 *   created from `PDFDocumentProxy.getOptionalContentConfig`. If `null`,
 *   the configuration will be fetched automatically with the default visibility
 *   states set.
 */
/**
 * PDF page operator list.
 *
 * @typedef {Object} PDFOperatorList
 * @property {Array<number>} fnArray - Array containing the operator functions.
 * @property {Array<any>} argsArray - Array containing the arguments of the
 *   functions.
 */
/**
 * Proxy to a `PDFPage` in the worker thread.
 */
class PDFPageProxy {