An empty commit message field now starts with the file `commit.template`
names (any git config level; `~/` and repository-relative paths resolve
as git resolves them), without its `#` comment lines, since commits keep
the message as written. It is filled when the repository opens or
changes and when a commit clears the field; a typed message is never
replaced, and a prepared merge / cherry-pick / revert message still
takes precedence.
Fixes#1285
l0ng-ai
a7708725cb