Fuzzing: check_signature mock can be fooled by a really short key.
Our mock function,
mock_crypto_pk_public_checksig__nocheck, fails to behave properly when it gets a ridiculously short key: the caller will have allocated a small amount, but we'll write a 20-byte digest.
This is causing a false positive on OSS-Fuzz.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information