paginate in offset mode when querying emoji - fixes #490

since the backend sorts emojis by name length when a query is present,
the normal pagination with `sinceId` / `untilId` would not work
reliably

`offsetMode` is better in this case, although it will produce
non-stable results if custom emojis that match the query are added or
removed while we paginate

packages/frontend/src/pages/custom-emojis-manager.vue

@@ -98,6 +98,9 @@ const selectedEmojis = ref<string[]>([]);
 const pagination = {
 	endpoint: 'admin/emoji/list' as const,
 	limit: 30,
+	offsetMode: computed(() => (
+		(query.value && query.value !== '') ? true : false
+	)),
 	params: computed(() => ({
 		query: (query.value && query.value !== '') ? query.value : null,
 	})),