Add a hard-coded filter for empty hashes

[misje]

When the SHA-256 hash e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855 exists in OpenCTI, a lot of noise is generated. There doesn't seem to be an easy way of preventing this useless indicator to end up in OpenCTI, so ignore this particular hash altogether in this integration.