Missing error handling in pkcs11_object_from_template

[ulrichb]

I'm talking about the following two lines:

https://github.com/OpenSC/libp11/blob/bb8b8389f39e61ee6508db86c1341495c06f9c9a/src/p11_key.c#L161-L162

Here a potential CK_INVALID_HANDLE from pkcs11_handle_from_template() is not handled.

=> We enter the following pkcs11_object_from_handle() with CK_INVALID_HANDLE.