Prevent JSON parse error (#827)

* Prevent JSON parse error

Users can pass in `{ enabled: true }` as the sortOptions, which means `initialSortBy` would be `undefined` and `JSON.parse` throws an error when you hand it `undefined`. So we need to default the value if it is not present.

* Update src/components/Table.vue

src/components/Table.vue

@@ -1582,7 +1582,7 @@ export default {
 
     initializeSort() {
       const { enabled, initialSortBy, multipleColumns } = this.sortOptions;
-      const initSortBy = JSON.parse(JSON.stringify(initialSortBy));
+      const initSortBy = JSON.parse(JSON.stringify(initialSortBy || {}));
 
       if (typeof enabled === 'boolean') {
         this.sortable = enabled;