libgit2 v0.27.4

This is a security release fixing out-of-bounds reads when
processing smart-protocol "ng" packets.

When parsing an "ng" packet, we keep track of both the current position
as well as the remaining length of the packet itself. But instead of
taking care not to exceed the length, we pass the current pointer's
position to strchr, which will search for a certain character until
hitting NUL. It is thus possible to create a crafted packet which
doesn't contain a NUL byte to trigger an out-of-bounds read.

The issue was discovered by the oss-fuzz project, issue 9406.