send-pack: fix capability-sending logic

send-pack: fix capability-sending logic

If we have capabilities to send to the server, we send the
regular "want" line followed by a NUL, then the
capabilities; otherwise, we do not even send the NUL.

However, when checking whether we want to send the "quiet"
capability, we check args->quiet, which is wrong. That flag
only tells us whether the client side wanted to be quiet,
not whether the server supports it (originally, in c207e34f,
it meant both; however, that was later split into two flags
by 01fdc21f).

We still check the right flag when actually printing
"quiet", so this could only have two effects:

  1. We might send the trailing NUL when we do not otherwise
     need to. In theory, an antique pre-capability
     implementation of git might choke on this (since the
     client is instructed never to respond with capabilities
     that the server has not first advertised).

  2. We might also want to send the quiet flag if the
     args->progress flag is false, but this code path would
     not trigger in that instance.

In practice, it almost certainly never matters. The
report-status capability dates back to 2005. Any real-world
server is going to advertise that, and we will always
respond with at least that capability.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>