httpfile does not check the return value of readhttphdr in getfilelength()

Reference: /n/sources/patch/httpfile-suicide
Date: Tue Mar 14 15:34:44 CET 2017
Signed-off-by: steve@quintile.net

--- /sys/src/cmd/ip/httpfile.c	Tue Mar 14 15:33:54 2017
+++ /sys/src/cmd/ip/httpfile.c	Tue Mar 14 15:33:52 2017
@@ -429,6 +429,9 @@
 		get, host);
 
 	status = readhttphdr(&netbio, &size);
+	if(status == nil)
+		return -1;
+
 	if(strstr(status, "200 OK") == nil){
 		werrstr("%s", status);
 		size = -1;