pyworker: empty flags are valid

Summary: Empty flags can be sent by Mercurial, do not error out in that case.

Reviewed By: quark-zju

Differential Revision: D20450124

fbshipit-source-id: c85af42be2afb95b09057583f6fec3a2a13d478a

eden/scm/edenscmnative/bindings/modules/pyworker/src/lib.rs

@@ -406,6 +406,8 @@ py_class!(class writerworker |py| {
             Some(UpdateFlag::Symlink)
         } else if flags == "x" {
             Some(UpdateFlag::Executable)
+        } else if flags == "" {
+            None
         } else {
             return Err(format_err!("Unknown flags: {}", flags)).map_pyerr(py);
         };