`decrypt_should_fail` spurious failure

[mversic]

This test seems to fail spuriously:

---- encryption::chacha20poly1305::tests::decrypt_should_fail stdout ----
thread 'encryption::chacha20poly1305::tests::decrypt_should_fail' panicked at crypto/src/encryption/chacha20poly1305.rs:111:48:
called `Result::unwrap_err()` on an `Ok` value: [72, 101, 108, 108, 111, 32, 97, 110, 100, 32, 71, 111, 111, 100, 98, 121, 101, 33]
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[DCNick3]

The problematic code is here. When ciphertext[1] is 0 the XOR doesn't do anything to the ciphertext[0] and the message turns out to be unexpectedly not corrupted.