Fixing addition of multiple categories for multiple users

src/EntryPoints/Specials/SpecialManageApprovers.php

@@ -67,7 +67,8 @@ private function handlePostRequest( WebRequest $request, array $approversCategor
 
 		$userWithCategories = array_filter( $approversCategories, fn( $approver ) => $approver->username === $username
 		);
-		$currentCategories = $userWithCategories[0]->categories ?? [];
+		$userWithCategories = reset( $userWithCategories );
+		$currentCategories = $userWithCategories !== false ? $userWithCategories->categories : [];
 
 		$this->processCategoryAction( $action, $category, $userId, $currentCategories );
 	}