Fix possible division by 0 in radius calculation

src/draw.c

@@ -412,6 +412,9 @@ static int layout_get_height(struct colored_layout *cl)
  */
 static int frame_internal_radius (int r, int w, int h)
 {
+        if (r == 0 || w == 0 || h == 0)
+                return 0;
+
         // Integer precision scaler, using 1/4 of int size
         const int s = 2 << (8 * sizeof(int) / 4);