fix hidden windows that start reappearing when the screen is resized.

Reference: /n/sources/patch/applied/rio-ghostwindows-fix
Date: Wed Apr 29 20:32:57 CES 2009
Signed-off-by: cinap_lenrek@gmx.de

--- /sys/src/cmd/rio/rio.c	Wed Apr 29 20:32:17 2009
+++ /sys/src/cmd/rio/rio.c	Wed Apr 29 20:32:07 2009
@@ -634,9 +634,10 @@
 				ishidden = 1;
 				break;
 			}
-		if(ishidden)
+		if(ishidden){
 			im = allocimage(display, r, screen->chan, 0, DWhite);
-		else
+			r = ZR;
+		}else
 			im = allocwindow(wscreen, r, Refbackup, DWhite);
 		if(im)
 			wsendctlmesg(w, Reshaped, r, im);