Helper::purge() protection (#392)

Author: dg

src/Framework/Helpers.php

@@ -20,6 +20,9 @@ class Helpers
 	 */
 	public static function purge(string $dir): void
 	{
+		if (preg_match('#^(\w:)?[/\\\\]?$#', $dir)) {
+			throw new \InvalidArgumentException('Directory must not be an empty string or root path.');
+		}
 		if (!is_dir($dir)) {
 			mkdir($dir);
 		}