drivers/wifi/esp_at: Fix system crash caused by null pointer

The code for checking the null pointer is incorrect,
with ESP_AT_CIPDINFO_USE turned on, after a soft reboot
of the host and before a reboot of ESP32, the host may
receive an incorrect IPD message causing a system crash.

Fixes #81804

Signed-off-by: Hongquan Li <[email protected]>

drivers/wifi/esp_at/esp.c

@@ -811,7 +811,7 @@ static int cmd_ipd_parse_hdr(struct esp_data *dev,
 	}
 
 	*sock = esp_socket_ref_from_link_id(dev, link_id);
-	if (!sock) {
+	if (*sock == NULL) {
 		LOG_ERR("No socket for link %ld", link_id);
 		return str - ipd_buf;
 	}