Simplify a few more branches to improve coverage (#500)

diff --git a/tests/test_crypto.py b/tests/test_crypto.py
index 2febb95..5b2c48a 100644
--- a/tests/test_crypto.py
+++ b/tests/test_crypto.py
@@ -802,6 +802,9 @@
         self.assertRaises(ValueError, key.generate_key, TYPE_RSA, -1)
         self.assertRaises(ValueError, key.generate_key, TYPE_RSA, 0)
 
+        with pytest.raises(TypeError):
+            key.generate_key(TYPE_RSA, object())
+
         # XXX RSA generation for small values of bits is fairly buggy in a wide
         # range of OpenSSL versions.  I need to figure out what the safe lower
         # bound for a reasonable number of OpenSSL versions is and explicitly