handle non-existing theme in user setting

src/Renderer/Twig/Extensions/Globals.php

@@ -6,6 +6,7 @@ use Engelsystem\Helpers\Authenticator;
 use Engelsystem\Http\Request;
 use Twig\Extension\AbstractExtension as TwigExtension;
 use Twig\Extension\GlobalsInterface as GlobalsInterface;
+use function array_key_exists;
 
 class Globals extends TwigExtension implements GlobalsInterface
 {
@@ -46,6 +47,10 @@ class Globals extends TwigExtension implements GlobalsInterface
             $themeId = (int)$query;
         }
 
+        if (array_key_exists($themeId, $themes) === false) {
+            $themeId = 1;
+        }
+
         $theme = $themes[$themeId];
 
         return [