mozilla/pdf.js — pull request #5488 by Snuffleupagus (2014-11-15 11:24:22+00:00)
Title: Prevent a "TypeError: pdfViewer is null" when the viewer loads (PR 5413 followup)

Currently if you manage to e.g. open the console (with Ctrl+Shift+K) before the viewer is initialized, the following will be printed in the console: `TypeError: pdfViewer is null`.
This doesn't cause any actual errors, but nevertheless it seems like something we should avoid.

Followup to PR #5413.