tests/test-issue1102.t

revlog: return 0 for the fast_rank of nullrev

By convention, the rank of the null revision is 0. This particular revision is
never "physically" stored in the changelog, so it is a special case.

For consistency, the value `None` is still being returned for revlogs which do
not store the fast_rank property for any revision.

Differential Revision: https://phab.mercurial-scm.org/D12208

  $ rm -rf a
  $ hg init a
  $ cd a
  $ echo a > a
  $ hg ci -Am0
  adding a
  $ hg tag t1 # 1
  $ hg tag --remove t1 # 2

  $ hg co 1
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg tag -f -r0 t1
  $ hg tags
  tip                                3:a49829c4fc11
  t1                                 0:f7b1eb17ad24

  $ cd ..