treat iconv issues

Signed-off-by: Arthur Schiwon <blizzz@arthur-schiwon.de>

apps/user_ldap/lib/Access.php

 	 * @throws \InvalidArgumentException
 	 */
 	public function sanitizeUsername($name) {
+		$name = trim($name);
+
 		if($this->connection->ldapIgnoreNamingRules) {
-			return trim($name);
+			return $name;
 		}
 
-		// Transliteration
-		// latin characters to ASCII
-		$name = iconv('UTF-8', 'ASCII//TRANSLIT', trim($name));
+		// Transliteration to ASCII
+		$transliterated = @iconv('UTF-8', 'ASCII//TRANSLIT', $name);
+		if($transliterated !== false) {
+			// depending on system config iconv can work or not
+			$name = $transliterated;
+		}
 
 		// Replacements
 		$name = str_replace(' ', '_', $name);

apps/user_ldap/tests/AccessTest.php

 	}
 
 	public function intUsernameProvider() {
+		// system dependent :-/
+		$translitExpected = @iconv('UTF-8', 'ASCII//TRANSLIT', 'fränk') ? 'frank' : 'frnk';
+
 		return [
 			['alice', 'alice'],
 			['b/ob', 'bob'],
 			['charly🐬', 'charly'],
 			['debo rah', 'debo_rah'],
 			['epost@poste.test', 'epost@poste.test'],
-			['fränk', 'frank'],
+			['fränk', $translitExpected],
 			[' gerda ', 'gerda'],
 			['🕱🐵🐘🐑', null]
 		];