Transaction parsing is broken

[orbitlens]

Describe the bug
TransactionBuilder.fromXDR call causes an error during parsing XDR for some transactions.

What version are you on?
8.1.1

To Reproduce

const {TransactionBuilder} = require("stellar-sdk")

TransactionBuilder.fromXDR('AAAAAgAAAABg/GhKJU5ut52ih6Klx0ymGvsac1FPJig1CHYqyesIHQAAJxACBmMCAAAADgAAAAAAAAABAAAAATMAAAAAAAABAAAAAQAAAABg/GhKJU5ut52ih6Klx0ymGvsac1FPJig1CHYqyesIHQAAAAAAAAAAqdkSiA5dzNXstOtkPkHd6dAMPMA+MSXwK8OlrAGCKasAAAAAAcnDgAAAAAAAAAAByesIHQAAAEAuLrTfW6D+HYlUD9y+JolF1qrb40hIRATzsQaQjchKJuhOZJjLO0d7oaTD3JZ4UL4vVKtV7TvV17rQgCQnuz8F', 'Public Global Stellar Network ; September 2015')

The code above causes an error

TypeError: medKey.ed25519 is not a function
  at Function.encodeEd25519PublicKey in stellar-base/lib/strkey.js — line 73
  at encodeMuxedAccountToAddress in stellar-base/lib/util/decode_encode_muxed_account.js — line 81
...

Possibly related to #645

Expected behavior
No error thrown.

Additional context
Looks like the problem emerged after upgrading to the latest stellar-sdk + stellar-base.

[Shaptic]

Thank you for this; it's resolved by stellar/js-stellar-base#429 and will be included in base-5.2.1 and subsequently the pending sdk-8.2.0