don't assume we get a ConfigureNotify event

If the window manager maps our window at the requested size, we may not get a
ConfigureNotify event.  This happens e.g. under ratpoison.

The result is that xw.uw and xw.uh are never set, so text is too small and
pngscale() tries to divide by 0.

sent.c

@@ -506,8 +506,7 @@ void xinit()
 		die("Can't open display.");
 	xw.scr = XDefaultScreen(xw.dpy);
 	xw.vis = XDefaultVisual(xw.dpy, xw.scr);
-	xw.w = DisplayWidth(xw.dpy, xw.scr);
-	xw.h = DisplayHeight(xw.dpy, xw.scr);
+	resize(DisplayWidth(xw.dpy, xw.scr), DisplayHeight(xw.dpy, xw.scr));
 
 	xw.attrs.background_pixel = WhitePixel(xw.dpy, xw.scr);
 	xw.attrs.bit_gravity = CenterGravity;