Trying to read a pdf file using PDFJS.getDocument function. The pdf worker is throwing


UnknownErrorException {
 name: "UnknownErrorException", 
 message: "Invalid root reference", 
 details: "FormatError: Invalid root reference"
}

The error can be easily reproduced calling PDFJS.getDocument(pdfUrl) using the attached pdf
[110229_10312017_6810306.pdf](https://github.com/mozilla/pdf.js/files/1444166/110229_10312017_6810306.pdf)


if (obj instanceof Ref) {
      return this.fetch(obj, suppressEncryption);
    }
    return obj;
  }
  fetch(ref, suppressEncryption = false) {
    if (!(ref instanceof Ref)) {
      throw new Error("ref object is not a reference");
    }
    const num = ref.num;
    
    
    
    const cacheEntry = this._cacheMap.get(num);
    if (cacheEntry !== undefined) {
      
      
      if (cacheEntry instanceof Dict && !cacheEntry.objId) {
        cacheEntry.objId = ref.toString();
      }
      return cacheEntry;
    }
    let xrefEntry = this.getEntry(num);
    if (xrefEntry === null) {