util: eliminate the possibility of returning None from `versiontuple()` This fixes the following error flagged by pytype: File "/mnt/c/Users/Matt/hg/mercurial/extensions.py", line 228, in load: unsupported operand types for > [unsupported-operands] Primitive types 'Optional[tuple]' and 'curver: Optional[tuple]' are not comparable. Differential Revision: https://phab.mercurial-scm.org/D11473

  $ cat >> $HGRCPATH << EOF
  > [extensions]
  > absorb=
  > drawdag=$TESTDIR/drawdag.py
  > EOF

  $ hg init
  $ hg debugdrawdag <<'EOS'
  > C
  > |
  > B
  > |
  > A
  > EOS

  $ hg phase -r A --public -q
  $ hg phase -r C --secret --force -q

  $ hg update C -q
  $ printf B1 > B

  $ hg absorb -aq

  $ hg log -G -T '{desc} {phase}'
  @  C secret
  |
  o  B draft
  |
  o  A public