getRangeReader(begin, end) {
    return null;
  }
Gets a reader for the range of the PDF data.

NOTE: Currently this method is only expected to be invoked *after*
the `IPDFStreamReader.prototype.headersReady` promise has resolved.

@param {number} begin - the start offset of the data.
@param {number} end - the end offset of the data.
@returns {IPDFStreamRangeReader}