When a smart HTTP server sends an error message via pkt-line, we detect
the error due to using PACKET_READ_DIE_ON_ERR_PACKET. This case was
added by 2d103c31 (pack-protocol.txt: accept error packets in any
context, 2018-12-29), but not covered by tests.
Signed-off-by: NJosh Steadmon <steadmon@google.com>
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>