move gotd fork into repo. (#111)

- update to latest telegram layer
- remove some references to fields in tg.Entities that don't exist in
the schema
- originally added here:
https://github.com/beeper/td/commit/820929062a2ba0104397bc01235ab58a9cff780e
  - referenced here
-
https://github.com/mautrix/telegramgo/commit/124f0967ed195b5a380c9bd02e170ada9710dde3
-
https://github.com/mautrix/telegramgo/commit/4205047aab2e0639217148b5d125bfaab668bd8e

pkg/gotd/telegram/downloader/cdn_test.go

@@ -0,0 +1,36 @@
+package downloader
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/tg"
+)
+
+func Test_cdn_decrypt(t *testing.T) {
+	testdata := make([]byte, 32)
+	tests := []struct {
+		name    string
+		key, iv []byte
+		err     bool
+	}{
+		{"Bad key", []byte{10}, nil, true},
+		{"Bad IV", make([]byte, 32), nil, true},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			c := &cdn{
+				redirect: &tg.UploadFileCDNRedirect{
+					EncryptionKey: test.key,
+					EncryptionIv:  test.iv,
+				},
+			}
+			_, err := c.decrypt(testdata, 0)
+			if test.err {
+				require.Error(t, err)
+			}
+		})
+	}
+}