Enabling pdfjs disableRange option prevents pdfs from loading

In ESR52, range-based requests in pdf.js (which allows pdfs to render-as-load) go out on the default circuit as the relevant code was running in the System security context. To 'fix' the issue, we simply disabled range-based request with the 'pdfjs.disableRange' option. However, in ESR60 based Tor Browser, enabling this option prevents PDFs from loading at all. Without the option enabled, PDFs load and render, but the range-based requests still go out on the default circuit.

Original bug: https://trac.torproject.org/projects/tor/ticket/15599