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.
%% no changes
%% no changes
%% uncompressed contents in repo
this is a test
%% uncompress our working dir copy
this is a test
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
%% uncompress our new working dir copy
this is a test