[vala] glib-2.0: Fix unescape_string and unescape_segment

[Jaap A. Haitsma <jhaitsma src gnome org>]

commit cfeb50378baf89362e50b9aa12b4a127198d2c62
Author: Jaap A. Haitsma <jaap haitsma org>
Date:   Sat Jul 11 18:44:26 2009 +0200

    glib-2.0: Fix unescape_string and unescape_segment
    
    Fixes bug #588011

 vapi/glib-2.0.vapi |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/vapi/glib-2.0.vapi b/vapi/glib-2.0.vapi
index fc4a92e..96da884 100644
--- a/vapi/glib-2.0.vapi
+++ b/vapi/glib-2.0.vapi
@@ -2483,8 +2483,8 @@ namespace GLib {
 
 		public static string parse_scheme (string uri);
 		public static string escape_string (string unescaped, string reserved_chars_allowed, bool allow_utf8);
-		public static string unescape_string (string escaped_string, string illegal_characters);
-		public static string unescape_segment (string escaped_string, string escaped_string_end, string illegal_characters);
+		public static string unescape_string (string escaped_string, string? illegal_characters = null);
+		public static string unescape_segment (string escaped_string, string escaped_string_end, string? illegal_characters = null);
 		[CCode (array_length = false, array_null_terminated = true)]
 		public static string[] list_extract_uris (string uri_list);
 	}