auth-manager: clarify _challenge_async()
auth-manager: clarify _challenge_async()

Keeping our own GSimpleAsyncResult rather than leaving it up to the
channel means _finish() doesn't have to worry about what happens if the
channel closes.

The g_assert_not_reached () is not safe, but is equivalent to the
previous behaviour (wrongly chaining up to the parent class makes it
assert). Next, a fix…

Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble