web/remux: correctly unset processing state

web/src/routes/remux/+page.svelte

@@ -43,7 +43,7 @@
     const render = async () => {
         if (!file || processing) return;
         await ff.init();
-
+        try {
             progress = '';
             processing = true;
 
@@ -71,15 +71,16 @@
                 args: ['-c', 'copy', '-map', '0']
             });
 
-        processing = false;
-
             if (render) {
                 openURL(URL.createObjectURL(render));
             } else {
                 console.log("not a valid file");
             }
 
+        } finally {
+            processing = false;
             file = undefined;
+        }
     };
 
     $: if (file) {