message: Megolm export: fix Android incompatibility
  I'd carefully added a workaround to maintain compatibility with the Android
  AES-CTR implementation... to the wrong thing.
diff: @@ -107,14 +107,14 @@ export function encryptMegolmKeyFile(data, password, options) {
  const salt = new Uint8Array(16);
  window.crypto.getRandomValues(salt);
  - // clear bit 63 of the salt to stop us hitting the 64-bit counter boundary
  - // (which would mean we wouldn't be able to decrypt on Android). The loss
  - // of a single bit of salt is a price we have to pay.
  - salt[9] &= 0x7f;
  -
  const iv = new Uint8Array(16);
  window.crypto.getRandomValues(iv);
  + // clear bit 63 of the IV to stop us hitting the 64-bit counter boundary
  + // (which would mean we wouldn't be able to decrypt on Android). The loss
  + // of a single bit of iv is a price we have to pay.
  + iv[9] &= 0x7f;
  +
  return deriveKeys(salt, kdf_rounds, password).then((keys) => {
  const [aes_key, hmac_key] = keys;
  