maintenance: core.commitGraph=false prevents writes
Recently, a user had an issue due to combining
fetch.writeCommitGraph=true with core.commitGraph=false. The root bug
has been resolved by preventing commit-graph writes when
core.commitGraph is disabled. This happens inside the 'git commit-graph
write' command, but we can be more aware of this situation and prevent
that process from ever starting in the 'commit-graph' maintenance task.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>