API: return error when no ports found (#16043)

When looking up device ports (get_port_graphs), return an error when no ports are found.

fixes #15964

includes/html/api_functions.inc.php

@@ -1070,6 +1070,10 @@ function get_port_graphs(Illuminate\Http\Request $request): JsonResponse
     $ports = $device->ports()->isNotDeleted()->hasAccess(Auth::user())
         ->select($columns)->orderBy('ifIndex')->get();
 
+    if ($ports->isEmpty()) {
+        return api_error(404, 'No ports found');
+    }
+
     return api_success($ports, 'ports');
 }