Fix caching error on Profile loading

To reproduce this
1. Set Caching to level 3
2. Load the board index

Warning: Trying to access array offset on value of type bool in /Sources/User.php on line 5372
Warning: Undefined array key "" in /Sources/User.php on line 5372

This is because $data is not set, which also causes a null compare.

Sources/User.php

@@ -5370,7 +5370,7 @@ protected static function loadUserData(array $users, int $type = self::LOAD_BY_I
 				}
 
 				// Does the cached data have everything we need?
-				if (self::$dataset_levels[$data['dataset']] >= self::$dataset_levels[$dataset]) {
+				if (is_array($data) && !empty(self::$dataset_levels[$data['dataset']]) && !empty(self::$dataset_levels[$dataset]) && self::$dataset_levels[$data['dataset']] >= self::$dataset_levels[$dataset]) {
 					self::$profiles[$id] = $data;
 					$loaded_ids[] = $id;
 					unset($users[$key]);