decode: raise an error when keygrip is missing

trezor_agent/gpg/decode.py

@@ -291,6 +291,7 @@ def load_by_keygrip(pubkey_bytes, keygrip):
         for p in packets:
             if p.get('keygrip') == keygrip:
                 return p, user_ids
+    raise KeyError('{} keygrip not found'.format(util.hexlify(keygrip)))
 
 
 def load_signature(stream, original_data):

trezor_agent/gpg/tests/test_decode.py

@@ -56,3 +56,8 @@ def test_has_custom_subpacket():
     for marker in custom_markers:
         sig = {'unhashed_subpackets': [marker]}
         assert decode.has_custom_subpacket(sig)
+
+
+def test_load_by_keygrip_missing():
+    with pytest.raises(KeyError):
+        decode.load_by_keygrip(pubkey_bytes=b'', keygrip=b'')