fix fencepost in buffer size calculation

Reference: /n/atom/patch/applied2013/vthostbuffence
Date: Fri Aug 23 05:30:43 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/vt/main.c	Fri Aug 23 05:30:33 2013
+++ /sys/src/cmd/vt/main.c	Fri Aug 23 05:30:34 2013
@@ -182,7 +182,7 @@
 		break;
 	}ARGEND;
 
-	host_buf = malloc(host_bsize);
+	host_buf = mallocz(host_bsize, 1);
 	hostp = host_buf;
 	hostlength = 0;
 
@@ -799,7 +799,7 @@
 set_host(Event *e)
 {
 	hostlength = e->n;
-	if(hostlength > host_bsize) {
+	while(hostlength >= host_bsize) {
 		host_bsize *= 2;
 		host_buf = realloc(host_buf,host_bsize);
 	}