devdraw: allow resize in xattach

The created window in xattach is missing the StructureNotifyMask,
if the WM does resize the window before mapping (like tiling WMs
do), the client will not get notified (and XGetWindowAttributes
in the same function will not get updated values)

Reproducible by starting acme in e.g. dwm.

src/cmd/devdraw/x11-screen.c

@@ -633,6 +633,7 @@ xattach(Client *client, char *label, char *winsize)
 		CWBackPixel|CWBorderPixel|CWColormap,
 		&attr		/* attributes (the above aren't?!) */
 	);
+	XSelectInput(_x.display, w->drawable, StructureNotifyMask | PropertyChangeMask);
 
 	/*
 	 * Label and other properties required by ICCCCM.