computed properties wont get filled at app-start

[fgerards]

With slower API server connections, the App fatals with errors inside the layouts/defaults.vue component.
Objects like "state.typo3.initial.navigtation[0] are not filled and there is no check to prevent errors on it.
Proposing following changes:

\<template\> \<div v-if="navMain !== null" class="wrapper"\> ... \<div v-if="breadcrumbs !== null" class="border-b mb-20px"\> ... computed: { ...mapState({ navMain: state => state.typo3.initial.navigation ? state.typo3.initial.navigation[0] : null, // get first instance from root tree, breadcrumbs: (state) => state.typo3.page.page ? state.typo3.page.page.breadcrumbs : null, // get breadcrumbs for current page

This secures, that if the without the axios-GET-Request being fired or resolved when component is rendered, the corresponding template parts are not rendered.

[tmotyl]

@fgerards can you send a PR?