Fix listing of '' and '/'.

runtime/bin/directory_macos.cc

Index: runtime/bin/directory_macos.cc
diff --git a/runtime/bin/directory_macos.cc b/runtime/bin/directory_macos.cc
index feb9a9ca8dec1a7045eaac9bef0a6badd322c3e2..94b495d7e466df7af32c5c68e715d7f5fcd57f03 100644
--- a/runtime/bin/directory_macos.cc
+++ b/runtime/bin/directory_macos.cc
@@ -79,11 +79,6 @@ ListType DirectoryListingEntry::Next(DirectoryListing* listing) {
   }
 
   if (lister_ == 0) {
-    if (!listing->path_buffer().Add(File::PathSeparator())) {
-      done_ = true;
-      return kListError;
-    }
-    path_length_ = listing->path_buffer().length();
     do {
       lister_ = reinterpret_cast<intptr_t>(
           opendir(listing->path_buffer().AsString()));
@@ -93,6 +88,12 @@ ListType DirectoryListingEntry::Next(DirectoryListing* listing) {
       done_ = true;
       return kListError;
     }
+    if (parent_ != NULL) {
+      if (!listing->path_buffer().Add(File::PathSeparator())) {
+        return kListError;
+      }
+    }
+    path_length_ = listing->path_buffer().length();
   }
   // Reset.
   listing->path_buffer().Reset(path_length_);