pull: Correctly handle repo->parent_repo when applying static deltas

In flatpak i was using a parent repo, and it failed to update
with ENOENT when dispatching an set-read-source opcode, because the
object it referenced was in the parent repo.

This fixes that by making _ostree_repo_read_bare_fd look
at parent_repo.

Closes: #362
Approved by: cgwalters

src/libostree/ostree-repo.c

@@ -2721,12 +2721,23 @@ _ostree_repo_read_bare_fd (OstreeRepo           *self,
 
   _ostree_loose_path (loose_path_buf, checksum, OSTREE_OBJECT_TYPE_FILE, self->mode);
 
-  *out_fd = openat (self->objects_dir_fd, loose_path_buf, O_RDONLY | O_CLOEXEC);
-  if (*out_fd < 0)
+  if (!ot_openat_ignore_enoent (self->objects_dir_fd, loose_path_buf, out_fd, error))
+    return FALSE;
+
+  if (*out_fd == -1)
     {
-      glnx_set_error_from_errno (error);
+      if (self->parent_repo)
+        return _ostree_repo_read_bare_fd (self->parent_repo,
+                                          checksum,
+                                          out_fd,
+                                          cancellable,
+                                          error);
+
+      g_set_error (error, G_IO_ERROR, G_IO_ERROR_NOT_FOUND,
+                   "No such file object %s", checksum);
       return FALSE;
     }
+
   return TRUE;
 }