Fix bug 8845: check the right length of memory in aes unit tests

This couldn't actually be a buffer overrun unless AES somehow turned
into memcpy, but still it's good to fix it.

changes/bug8845

@@ -0,0 +1,3 @@
+  o Minor bugfixes (test):
+    - Fix an impossible buffer overrun in the AES unit tests. Fixes bug 8845;
+      bugfix on 0.2.0.7-alpha. Found by eugenis.

src/test/test_crypto.c

@@ -730,7 +730,7 @@ test_crypto_aes_iv(void *arg)
   /* Decrypt with the wrong key. */
   decrypted_size = crypto_cipher_decrypt_with_iv(key2, decrypted2, 4095,
                                              encrypted1, encrypted_size);
-  test_memneq(plain, decrypted2, encrypted_size);
+  test_memneq(plain, decrypted2, decrypted_size);
   /* Alter the initialization vector. */
   encrypted1[0] += 42;
   decrypted_size = crypto_cipher_decrypt_with_iv(key1, decrypted1, 4095,