If there is an error in initializing ChaCha20 cipher with OpenSSL, an invalid
error code is returned. This can happen if there is an heap exhaustion. This
error is not correctly detected and could allow libssh to use partially
initialized cipher context.

This is caused by the mismatch of return value meaning from OpenSSL and libssh,
where OpenSSL error (rv=0) aliases with SSH_OK (0) and is returned directly
from the function chacha20_poly1305_set_key(). This will likely cause error
somewhere down the road.