GHSA-2vh6-hw4j-32ww: gix-packetline: reachable panic on empty side-band packet (pre-auth network DoS)

gix-packetline panics when it receives a side-band packet line that contains only the band-id byte with an empty payload. A malicious Git server - or any remote a victim clones/fetches from - can abort the gix client process during a normal fetch. This is a pre-authentication, network-triggered denial of service.