fix invalid date on admin ui report create

src/app/admin/reports/SidebarActions.svelte

@@ -61,7 +61,7 @@
         key: 'createdAt',
         type: 'checkbox',
         label: 'Report kann bearbeitet werden',
-        options: { convert: (v) => (v ? new Date().toISOString() : null) }
+        options: { convert: (v) => (v ? null : new Date().toISOString()) }
       }
     ]
   ]}