fix 'convert' with single commit repositories
The attached patch passes the three 'convert' testcases, and also is
able to successfully convert the git.git repository.
adding a
% check custom patch options are honored
requesting all changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
applying ../a.diff
Using custom patch
nothing changed