sync: Don't process project.list in a mirror

We have no working tree, so we cannot update the project.list
state file, nor should we try to delete a directory if a project is
removed from the manifest.  Clients would still need the repository
for historical records.

Signed-off-by: Shawn O. Pearce <sop@google.com>

subcmds/sync.py

@@ -217,6 +217,10 @@ uncommitted changes are present' % project.relpath
             missing.append(project)
         self._Fetch(missing)
 
+    if self.manifest.IsMirror:
+      # bail out now, we have no working tree
+      return
+
     if self.UpdateProjectList():
       sys.exit(1)