internal/gomote: fix panic in ListDirectoryStreaming

For golang/go#69732

Change-Id: I72ef0672cfffa7d33afd44f886c67933242801fb
Reviewed-on: https://go-review.googlesource.com/c/build/+/617515
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

internal/gomote/swarming.go

@@ -356,7 +356,7 @@ func (ss *SwarmingServer) ListDirectoryStreaming(req *protos.ListDirectoryReques
 	for i := 0; i < len(entries); i += chunkSize {
 		end := min(chunkSize, len(entries[i:]))
 		if err := stream.Send(&protos.ListDirectoryResponse{
-			Entries: entries[i:end],
+			Entries: entries[i : i+end],
 		}); err != nil {
 			return err
 		}