fix: Fix small psalm errors in FTP and LDAP connections

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

apps/files_external/lib/Lib/Storage/FtpConnection.php

@@ -50,10 +50,7 @@ class FtpConnection {
 	}
 
 	public function __destruct() {
-		if ($this->connection) {
-			ftp_close($this->connection);
-		}
-		$this->connection = null;
+		ftp_close($this->connection);
 	}
 
 	public function setUtf8Mode(): bool {

apps/user_ldap/lib/Connection.php

@@ -446,8 +446,7 @@ class Connection extends LDAPUtility {
 
 	private function doCriticalValidation(): bool {
 		$configurationOK = true;
-		$errorStr = 'Configuration Error (prefix '.
-			(string)$this->configPrefix .'): ';
+		$errorStr = 'Configuration Error (prefix ' . $this->configPrefix . '): ';
 
 		//options that shall not be empty
 		$options = ['ldapHost', 'ldapUserDisplayName',