fix: check if wallet has master_private_keys

lib/wallet.py

@@ -816,6 +816,7 @@ class Abstract_Wallet(object):
             imported_account.update_password(old_password, new_password)
             self.save_accounts()
 
+        if hasattr(self, 'master_private_keys'):
             for k, v in self.master_private_keys.items():
                 b = pw_decode(v, old_password)
                 c = pw_encode(b, new_password)