Use correct length for offsetting extra nonce and remaining data.

cgminer.c

@@ -1361,8 +1361,8 @@ static void calc_midstate(struct work *work)
  * entered under gbt_lock */
 static void __build_gbt_coinbase(struct pool *pool)
 {
+	int cbt_len, cal_len, orig_len;
 	unsigned char *coinbase;
-	int cbt_len, cal_len;
 	uint8_t *extra_len;
 
 	cbt_len = strlen(pool->coinbasetxn) / 2;
@@ -1374,10 +1374,11 @@ static void __build_gbt_coinbase(struct pool *pool)
 	coinbase = calloc(cal_len, 1);
 	hex2bin(coinbase, pool->coinbasetxn, 42);
 	extra_len = (uint8_t *)(coinbase + 41);
-	hex2bin(coinbase + 42, pool->coinbasetxn + 84, *extra_len);
-	memcpy(coinbase + 42 + *extra_len, &pool->nonce2, 4);
+	orig_len = *extra_len;
+	hex2bin(coinbase + 42, pool->coinbasetxn + 84, orig_len);
+	memcpy(coinbase + 42 + orig_len, &pool->nonce2, 4);
 	*extra_len += 4;
-	hex2bin(coinbase + 42 + *extra_len, pool->coinbasetxn + 84 + (*extra_len * 2), cbt_len - *extra_len - 42);
+	hex2bin(coinbase + 42 + *extra_len, pool->coinbasetxn + 84 + (orig_len * 2), cbt_len - orig_len - 42);
 	pool->nonce2++;
 	free(pool->gbt_coinbase);
 	pool->gbt_coinbase = coinbase;