if a rio attach failed (due to an overly large rectangle, for instance),
the fid was still marked as busy, confusing subsequent
9p requests.

Reference: /n/sources/patch/applied/rioattach
Date: Thu Dec 16 14:59:03 CET 2004

--- /sys/src/cmd/rio/xfid.c	Thu Dec 16 14:59:04 2004
+++ /sys/src/cmd/rio/xfid.c	Thu Dec 16 14:59:03 2004
@@ -208,6 +208,7 @@
 	x->f->w = w;
 	if(w == nil){
 		qunlock(&all);
+		x->f->busy = FALSE;
 		filsysrespond(x->fs, x, &t, err);
 		return;
 	}