Empty config sections are neither deleted nor reused

[Jonas Bernoulli <jonas@bernoul.li>]

After running

  git init .
  git config foo.bar baz
  git config --unset foo.bar    # 1
  git config foo.bar baz        # 2

.git/config contains

  [core]
          repositoryformatversion = 0
          filemode = true
          bare = false
          logallrefupdates = true
  [foo]
  [foo]
          bar = baz

(1) did not remove the "foo" section when the last contained variable
was unset and (2) did not reuse the empty "foo" section when "foo.bar"
was set again.

I would prefer if unsetting the last variable in a section would cause
the heading of the now empty section would be removed.

But it might also make sense to not remove an empty section and to
instead reuse an empty section.  That would prevent a section from being
moved to eof because it became temporarily empty.  Maybe that was the
intention and Git at some point stopped re-using an empty section?

It could even be argued that it would make sense for empty sections to
be removed *and* reused (in order to "cleanup" old empty sections).

The only possible combination which doesn't make sense is to not remove
an empty section and to also not reuse an empty section - unfortunately
that's what Git currently does.

  Best regards,
  Jonas