spi25.c: Add a null check

Change-Id: I5fcc23d81b8404af90768afa2954509bf334ab2c
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/39974
Original-Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>
Original-Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/71734
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
diff --git a/spi25.c b/spi25.c
index 734df28..b13318b 100644
--- a/spi25.c
+++ b/spi25.c
@@ -441,6 +441,8 @@
 		msg_cerr("%s called for too long a write\n", __func__);
 		return 1;
 	}
+	if (!out_bytes && out_len > 0)
+		return 1;
 
 	memcpy(cmd + 1 + addr_len, out_bytes, out_len);
 	cmds[1].writecnt = 1 + addr_len + out_len;