convert/svn: make sink recover gracefully from empty changeset
Otherwise when processing a changeset that in fact changes no files
(perhaps due to bug in import from CVS) can get something like:
unexpected svn output:
abort: unable to cope with svn output
Bug report and patch draft by Jesse Glick <jesse.glick@sun.com>
adding a
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
% push should push to default when default-push not set
pushing
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
% push should push to default-push when set
pushing
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files