Changeset f23d387 in Launcher

Fix bad logic surrounding download resuming

An oversight in the implementation of partial download resumption led
to cross-contamination in the presence of multiple request URLs, where
an Accept-Ranges header from one server would cause a Range header
to be supplied to the next. Compounded with a bad ternary expression
in HttpRequest which couldn't handle non-200 success codes, this
was causing cryptic "Stream closed" errors on library downloads.