[PATCH] cmd: pxe_utils: fix ipappend ip config empty vars

[Artem Lapkin <email2tema@gmail.com>]

PROBLEM: If ipaddr, serverip, gatewayip or netmask variable undefined
we can have for example ip=192.168.2.33:<NULL>:192.168.2.1:255.255.255.0
yes its works same for linux kernel, but im think no need print <NULL>

SUGGESTED SOLUTION:
if some variable was undefined we need just print empty place like this
ip=192.168.2.33::192.168.2.1:255.255.255.0

Signed-off-by: Artem Lapkin <art@khadas.com>

---
 cmd/pxe_utils.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/cmd/pxe_utils.c b/cmd/pxe_utils.c
index 8716e782..2049c0f3 100644
--- a/cmd/pxe_utils.c
+++ b/cmd/pxe_utils.c
@@ -395,9 +395,12 @@ static int label_boot(struct cmd_tbl *cmdtp, struct pxe_label *label)
 	}
 
 	if (label->ipappend & 0x1) {
+		char *a = env_get("ipaddr");
+		char *b = env_get("serverip");
+		char *c = env_get("gatewayip");
+		char *d = env_get("netmask");
 		sprintf(ip_str, " ip=%s:%s:%s:%s",
-			env_get("ipaddr"), env_get("serverip"),
-			env_get("gatewayip"), env_get("netmask"));
+			a ? a : "", b ? b : "", c ? c : "", d ? d : "");
 	}
 
 #ifdef CONFIG_CMD_NET
-- 
2.25.1