Rev 1389: fix upgrading of trees with no commits in /home/robertc/source/baz/bzr-integration

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revno: 1389
revision-id: robertc at robertcollins.net-20051024135918-024629d7ee347b5c
parent: robertc at robertcollins.net-20051024085433-5e48ed93d1546627
parent: dilinger at athenacr.com-20051020194856-86687868337effed
committer: Robert Collins <robertc at robertcollins.net>
timestamp: Mon 2005-10-24 23:59:18 +1000
message:
  fix upgrading of trees with no commits
modified:
  bzrlib/upgrade.py              history2weaves.py-20050818063535-e7d319791c19a8b2
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    merged: dilinger at athenacr.com-20051020194856-86687868337effed
    parent: mbp at sourcefrog.net-20051020035533-aeb2314d74708a3d
    committer: Andres Salomon <dilinger at athenacr.com>
    timestamp: Thu 2005-10-20 15:48:56 -0400
    message:
      Handle the case where revision_history() returns an empty list during
      an upgrade.  Not a huge problem, since there's really nothing to convert,
      but it's nice to not spew errors anyways.