Add a dummy call to BN_rand_ex() in the FIPS provider

The previous commit made BIGNUM RAND operations available from within
the FIPS provider. We test this out by making a dummy call to check it
completes successfully.

Reviewed-by: Matthias St. Pierre <[email protected]>
(Merged from openssl#9193)

Author: mattcaswell

providers/fips/fipsprov.c

@@ -120,6 +120,9 @@ static int dummy_evp_call(void *provctx)
     if (RAND_DRBG_bytes(drbg, randbuf, sizeof(randbuf)) <= 0)
         goto err;
 
+    if (!BN_rand_ex(a, 256, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY, bnctx))
+        goto err;
+
     ret = 1;
  err:
     BN_CTX_end(bnctx);