Move server view management parts to new controller and clean up code

app/Http/Middleware/Admin/Servers/ServerInstalled.php

@@ -0,0 +1,40 @@
+<?php
+
+namespace Pterodactyl\Http\Middleware\Admin\Servers;
+
+use Closure;
+use Illuminate\Http\Request;
+use Illuminate\Http\Response;
+use Pterodactyl\Models\Server;
+use Symfony\Component\HttpKernel\Exception\HttpException;
+use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
+
+class ServerInstalled
+{
+    /**
+     * Checks that the server is installed before allowing access through the route.
+     *
+     * @param \Illuminate\Http\Request $request
+     * @param \Closure $next
+     * @return mixed
+     */
+    public function handle(Request $request, Closure $next)
+    {
+        /** @var \Pterodactyl\Models\Server|null $server */
+        $server = $request->route()->parameter('server');
+
+        if (! $server instanceof Server) {
+            throw new NotFoundHttpException(
+                'No server resource was located in the request parameters.'
+            );
+        }
+
+        if ($server->installed !== 1) {
+            throw new HttpException(
+                Response::HTTP_FORBIDDEN, 'Access to this resource is not allowed due to the current installation state.'
+            );
+        }
+
+        return $next($request);
+    }
+}