Fix redirect on logout

An instance may restrict access to the public timeline (among others)
to authenticated users and there already is a setting to decide which page
to show authenticated and unauthenticated viewers by default each.
However, the logout redirect didn't honour this setting
leading to potentially broken pages and errors on logout

src/components/settings_modal/settings_modal.js

@@ -69,7 +69,7 @@ const SettingsModal = {
       this.$store.dispatch('closeSettingsModal')
     },
     logout () {
-      this.$router.replace('/main/public')
+      this.$router.replace(this.$store.state.instance.redirectRootNoLogin || '/main/all')
       this.$store.dispatch('closeSettingsModal')
       this.$store.dispatch('logout')
     },