Fix directory-listing to return a future on cancel.

runtime/bin/directory.cc

Index: runtime/bin/directory.cc
diff --git a/runtime/bin/directory.cc b/runtime/bin/directory.cc
index 058d6382b837f5b52c20cefd0c6234fb597a4794..01f9f758d052b50205f8c00b6494f6daa7ed2a68 100644
--- a/runtime/bin/directory.cc
+++ b/runtime/bin/directory.cc
@@ -262,6 +262,9 @@ CObject* Directory::ListNextRequest(const CObjectArray& request) {
     CObjectIntptr ptr(request[0]);
     AsyncDirectoryListing* dir_listing =
         reinterpret_cast<AsyncDirectoryListing*>(ptr.Value());
+    if (dir_listing->IsEmpty()) {
+      return new CObjectArray(CObject::NewArray(0));
+    }
     const int kArraySize = 128;
     CObjectArray* response = new CObjectArray(CObject::NewArray(kArraySize));
     dir_listing->SetArray(response, kArraySize);