keystore: "old"-type seeds cannot have a passphrase

related: https://github.com/spesmilo/electrum/pull/8906

electrum/keystore.py

@@ -1159,6 +1159,8 @@ def purpose48_derivation(account_id: int, xtype: str) -> str:
 def from_seed(seed, passphrase, is_p2sh=False):
     t = seed_type(seed)
     if t == 'old':
+        if passphrase:
+            raise Exception("'old'-type electrum seed cannot have passphrase")
         keystore = Old_KeyStore({})
         keystore.add_seed(seed)
     elif t in ['standard', 'segwit']:

electrum/plugins/trustedcoin/trustedcoin.py

@@ -565,8 +565,8 @@ class TrustedCoinPlugin(BasePlugin):
                 # note: pre-2.7 2fa seeds were typically 24-25 words, however they
                 # could probabilistically be arbitrarily shorter due to a bug. (see #3611)
                 # the probability of it being < 20 words is about 2^(-(256+12-19*11)) = 2^(-59)
-                if passphrase != '':
-                    raise Exception('old 2fa seed cannot have passphrase')
+                if passphrase:
+                    raise Exception("old '2fa'-type electrum seed cannot have passphrase")
                 xprv1, xpub1 = self.get_xkeys(' '.join(words[0:12]), t, '', "m/")
                 xprv2, xpub2 = self.get_xkeys(' '.join(words[12:]), t, '', "m/")
             elif n == 12:  # new scheme