[ticket/13454] Add excessively removed code back

PHPBB3-13454

phpBB/includes/functions_content.php

@@ -763,6 +763,8 @@ function make_clickable_callback($type, $whitespace, $url, $relative_url, $class
 		// set last_char to empty here, so the variable can be used later to
 		// check whether a character was removed
 		default:
+			$last_char = '';
+		break;
 	}
 
 	$short_url = (utf8_strlen($url) > 55) ? utf8_substr($url, 0, 39) . ' ... ' . utf8_substr($url, -10) : $url;