do not try to draw 0 width/height windows

Ref: #76 (comment)

Author: N-R-K

src/selection_wind.c

@@ -94,6 +94,9 @@ void selectionWindDraw(void)
             opt.lineWidth }
     };
 
+    if (sel->rect.w == 0 || sel->rect.h == 0)
+        return;
+
     for (size_t i = 0; i < ARRAY_COUNT(pw->windows); ++i) {
         XRectangle *rp = rects + i;
         XMoveResizeWindow(disp, pw->windows[i], rp->x, rp->y, rp->width, rp->height);