from sources.  toss packets immediately if not connected.

Reference: /n/atom/patch/applied/oventincpkt
Date: Thu Mar 20 15:35:49 CET 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/libventi/rpc.c	Thu Mar 20 15:35:31 2014
+++ /sys/src/libventi/rpc.c	Thu Mar 20 15:35:31 2014
@@ -37,6 +37,12 @@
 	uchar tag, buf[2], *top;
 	Rwait *r, *rr;
 
+	if(z == nil){
+		werrstr("not connected");
+		packetfree(p);
+		return nil;
+	}
+
 	/* must malloc because stack could be private */
 	r = vtmallocz(sizeof(Rwait));