rust: Add assertion that input length is at least 0 for AES

It doesn't look like the AES engine can handle 0-sized input. This makes
sense, in a way, as it is an edge case and in most cases a no-op. Only
in GCM mode, where there one might want to compute a tag over a 0-byte
input, would this come up.

rust/k210-shared/src/soc/aes.rs

@@ -53,6 +53,7 @@ pub fn run(
         tag: &mut [u8],
     )
 {
+    assert!(ind.len() != 0);
     match cipher_mode {
         cipher_mode::ECB => assert!(iv.len() == 0 && aad.len() == 0),
         cipher_mode::CBC => assert!(iv.len() == 16 && aad.len() == 0),