Fix duplication for Octane (#51)

* Update SetTheme.php

Fixes Octane duplication issue

* Update SetTheme.php

Better approach! Dont even add if its already there

src/Http/Middleware/SetTheme.php

@@ -33,15 +33,24 @@ public function handle(Request $request, Closure $next): Response
             return $next($request);
         }
 
-        $panel->userMenuItems(
-            ThemesPlugin::canView() ?
-            [
-                MenuItem::make('Themes')
-                    ->label(__('themes::themes.themes'))
-                    ->icon(config('themes.icon'))
-                    ->url(ThemesPage::getUrl()),
-            ] : []
-        );
+        /**
+         * Important for Laravel Octane!
+         * 
+         * Check if item already exists before adding it
+         * to the menu items.
+         */
+        if(!isset($panel->getUserMenuItems()[__('themes::themes.themes')])){
+            $panel->userMenuItems(
+                ThemesPlugin::canView() ?
+                    [
+                        __('themes::themes.themes') =>
+                        MenuItem::make('Themes')
+                            ->label(__('themes::themes.themes'))
+                            ->icon(config('themes.icon'))
+                            ->url(ThemesPage::getUrl()),
+                    ] : []
+            );
+        }
 
         FilamentColor::register($themes->getCurrentThemeColor());