mozilla/pdf.js — pull request #4693 by Snuffleupagus (2014-04-27 10:03:08+00:00)
Title: Ensure that the viewer loads even if there are errors when the preferences are read

While trying to debug #4690, I stumbled on another issue.
Currently if e.g. `Preferences._readFromStorage` fails, the PDF document will fail to load. This PR adds missing rejection handler functions, to avoid this issue. (I assumed that it was best to handle this on the callee side.)