Fix buffer overflow reported by cinap_lenrek@gmx.de:
"1:2:3:4:5:6:6:255.255.255.255 writes two bytes beyond the ip buffer".


Reference: /n/sources/patch/applied/parseip-overflow
Date: Wed May  8 12:14:41 CES 2013
Signed-off-by: miller@hamnavoe.com

--- /sys/src/libip/parseip.c	Wed May  8 12:13:41 2013
+++ /sys/src/libip/parseip.c	Wed May  8 12:13:39 2013
@@ -73,7 +73,8 @@
 	for(i = 0; i < IPaddrlen && ipcharok(*p); i+=2){
 		op = p;
 		x = strtoul(p, &p, 16);
-		if(*p == '.' || (*p == 0 && i == 0)){	/* ends with v4? */
+		if((*p == '.' && i <= IPaddrlen-4) || (*p == 0 && i == 0)){
+			/* ends with v4 */
 			p = v4parseip(to+i, op);
 			i += 4;
 			break;