Don't wait for complete

In some cases (e.g. the net error page) the window.onload event never fires
and document.readyState never changes to complete.

See:
 - https://bugzil.la/444165
 - http://hg.mozilla.org/mozilla-central/file/a57801cec8be/docshell/resources/content/netError.xhtml#l374
use the inline JSON for the default locale, too

Due to CSP, about:neterror cannot have any non-inline resources.  The only
thing it can have is the inline JSON, even for the default locale.  So we need
a way to use the inline resources with the default locale.