test: increase coverage of Buffer.transcode

Adds test for transcoding an empty buffer. PR-URL: #10437 Reviewed-By: Rich Trott <rtrott@gmail.com> Reviewed-By: Evan Lucas <evanlucas@me.com> Reviewed-By: Michaël Zasso <targos@protonmail.com> Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>

Author: joyeecheung

test/parallel/test-icu-transcode.js

@@ -70,3 +70,8 @@ assert.deepStrictEqual(
  buffer.transcode(uint8array, 'latin1', 'utf16le'),
  Buffer.from('hä', 'utf16le'));
 }
+
+{
+ const dest = buffer.transcode(new Uint8Array(), 'utf8', 'latin1');
+ assert.strictEqual(dest.length, 0);
+}