fix: another let const svelte issue

Author: sashamilenkovic

frameworks/svelte/JS/src/pages/WatermarksPage.svelte

@@ -6,7 +6,7 @@ import {
   unloadWatermarksViewer,
 } from "../nutrient/watermarks/implementation";
 
-const container = null;
+let container = null;
 
 let nutrientViewer = null;