Handle new style recordings

Newer recordings are always binary and don't include the encoding
specifier.

tests/playback-ui.js

@@ -47,6 +47,8 @@ function enableUI() {
     startButton.addEventListener('click', start);
 
     frames = VNC_frame_data;
+    // Only present in older recordings
+    if (window.VNC_frame_encoding)
         encoding = VNC_frame_encoding;
 }