fix: Fix small psalm errors in legacy

Signed-off-by: Côme Chilliet <come.chilliet@nextcloud.com>

lib/private/legacy/OC_Files.php

@@ -104,7 +104,7 @@ class OC_Files {
 	 * return the content of a file or return a zip file containing multiple files
 	 *
 	 * @param string $dir
-	 * @param string $files ; separated list of files to download
+	 * @param string|array $files ; separated list of files to download
 	 * @param array $params ; 'head' boolean to only send header of the request ; 'range' http range header
 	 */
 	public static function get($dir, $files, $params = null) {

lib/private/legacy/OC_Helper.php

@@ -138,7 +138,7 @@ class OC_Helper {
 
 		$bytes = (float)$str;
 
-		if (preg_match('#([kmgtp]?b?)$#si', $str, $matches) && !empty($bytes_array[$matches[1]])) {
+		if (preg_match('#([kmgtp]?b?)$#si', $str, $matches) && isset($bytes_array[$matches[1]])) {
 			$bytes *= $bytes_array[$matches[1]];
 		} else {
 			return false;