e_rc4_hmac_md5.c: harmonize zero-length fragment handling with

e_aes_cbc_hmac_sha1.c (mostly for aesthetic reasons).

crypto/evp/e_rc4_hmac_md5.c

@@ -75,6 +75,8 @@ typedef struct
     size_t		payload_length;
     } EVP_RC4_HMAC_MD5;
 
+#define NO_PAYLOAD_LENGTH	((size_t)-1)
+
 void rc4_md5_enc (RC4_KEY *key, const void *in0, void *out,
 		MD5_CTX *ctx,const void *inp,size_t blocks);
 
@@ -93,7 +95,7 @@ static int rc4_hmac_md5_init_key(EVP_CIPHER_CTX *ctx,
 	key->tail = key->head;
 	key->md   = key->head;
 
-	key->payload_length = 0;
+	key->payload_length = NO_PAYLOAD_LENGTH;
 
 	return 1;
 	}
@@ -122,10 +124,10 @@ static int rc4_hmac_md5_cipher(EVP_CIPHER_CTX *ctx, unsigned char *out,
 #endif
 	size_t	plen = key->payload_length;
 
-	if (plen && len!=(plen+MD5_DIGEST_LENGTH)) return 0;
+	if (plen!=NO_PAYLOAD_LENGTH && len!=(plen+MD5_DIGEST_LENGTH)) return 0;
 
 	if (ctx->encrypt) {
-		if (plen==0) plen = len;
+		if (plen==NO_PAYLOAD_LENGTH) plen = len;
 #if defined(STITCHED_CALL)
 		/* cipher has to "fall behind" */
 		if (rc4_off>md5_off) md5_off+=MD5_CBLOCK;
@@ -190,7 +192,7 @@ static int rc4_hmac_md5_cipher(EVP_CIPHER_CTX *ctx, unsigned char *out,
 #endif
 		/* decrypt HMAC at once */
 		RC4(&key->ks,len-rc4_off,in+rc4_off,out+rc4_off);
-		if (plen) {	/* "TLS" mode of operation */
+		if (plen!=NO_PAYLOAD_LENGTH) {	/* "TLS" mode of operation */
 			MD5_Update(&key->md,out+md5_off,plen-md5_off);
 
 			/* calculate HMAC and verify it */
@@ -206,7 +208,7 @@ static int rc4_hmac_md5_cipher(EVP_CIPHER_CTX *ctx, unsigned char *out,
 		}
 	}
 
-	key->payload_length = 0;
+	key->payload_length = NO_PAYLOAD_LENGTH;
 
 	return 1;
 	}