Fix WeDo2.send sends empty message

WeDo2.send invokes Base64Util.uint8ArrayToBase64(message). However message.arrayLength === undefined. This causes Base64Util.uint8ArrayToBase64 always returning empty string ''.

src/extensions/scratch3_wedo2/index.js

@@ -664,7 +664,7 @@ class WeDo2 {
         return this._ble.write(
             BLEService.IO_SERVICE,
             uuid,
-            Base64Util.uint8ArrayToBase64(message),
+            Base64Util.uint8ArrayToBase64(new Uint8Array(message)),
             'base64'
         );
     }