Directly return from final sha3/keccak_final if no bytes are requested

Requesting zero bytes from shake previously led to out-of-bounds write
on some platforms.
Signed-off-by: NPatrick Steuer <patrick.steuer@de.ibm.com>
Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/9433)

(cherry picked from commit a890ef833d114da3430c2f2efd95e01714704d34)

crypto/evp/m_sha3.c

@@ -108,6 +108,9 @@ static int sha3_final(EVP_MD_CTX *evp_ctx, unsigned char *md)
     size_t bsz = ctx->block_size;
     size_t num = ctx->num;
 
+    if (ctx->md_size == 0)
+        return 1;
+
     /*
      * Pad the data with 10*1. Note that |num| can be |bsz - 1|
      * in which case both byte operations below are performed on