Fixed crash on public entitiy viewing

tests/PublicViewTest.php

@@ -0,0 +1,41 @@
+<?php
+
+class PublicViewTest extends TestCase
+{
+
+    public function testBooksViewable()
+    {
+        $this->setSettings(['app-public' => 'true']);
+        $books = \BookStack\Book::orderBy('name', 'asc')->take(10)->get();
+        $bookToVisit = $books[1];
+
+        // Check books index page is showing
+        $this->visit('/books')
+            ->seeStatusCode(200)
+            ->see($books[0]->name)
+            // Check indavidual book page is showing and it's child contents are visible.
+            ->click($bookToVisit->name)
+            ->seePageIs($bookToVisit->getUrl())
+            ->see($bookToVisit->name)
+            ->see($bookToVisit->chapters()->first()->name);
+    }
+
+    public function testChaptersViewable()
+    {
+        $this->setSettings(['app-public' => 'true']);
+        $chapterToVisit = \BookStack\Chapter::first();
+        $pageToVisit = $chapterToVisit->pages()->first();
+
+        // Check chapters index page is showing
+        $this->visit($chapterToVisit->getUrl())
+            ->seeStatusCode(200)
+            ->see($chapterToVisit->name)
+            // Check indavidual chapter page is showing and it's child contents are visible.
+            ->see($pageToVisit->name)
+            ->click($pageToVisit->name)
+            ->see($chapterToVisit->book->name)
+            ->see($chapterToVisit->name)
+            ->seePageIs($pageToVisit->getUrl());
+    }
+
+}