[var] Minor lifecycle adjustment

src/hb-font.cc

@@ -1556,11 +1556,11 @@ hb_font_set_var_coords_normalized (hb_font_t *font,
   if (unlikely (coords_length && !copy))
     return;
 
-  free (font->coords);
-
   if (coords_length)
     memcpy (copy, coords, coords_length * sizeof (coords[0]));
 
+  free (font->coords);
+
   font->coords = copy;
   font->num_coords = coords_length;
 }