Previously supplying an invalid url for download would result in
uclient_new returning NULL and crash the autoupdater as soon as
cl->priv is accessed.
Signed-off-by: Tobias Schramm <email@example.com>
This new version of the autoupdater is implemented in C instead of Lua,
allowing us to interface with libuclient (HTTP downloads) and libecdsautil
(signature checks) directly instead of spawning external processes,
saving RAM and making error handling more robust.
[Matthias Schiffer: add commit message]