nil not 0

Reference: /n/atom/patch/applied/wcnit
Date: Sat May  3 05:51:14 CES 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/wc.c	Sat May  3 05:51:07 2014
+++ /sys/src/cmd/wc.c	Sat May  3 05:51:08 2014
@@ -37,7 +37,7 @@
 		pchar = 1;
 	}
 	if(argc==0)
-		count(0, 0);
+		count(0, nil);
 	else{
 		for(i=0;i<argc;i++){
 			f=open(argv[i], OREAD);