[libsoup] soup-message-headers: Add a missing (optional) annotation

[Philip Withnall <pwithnall src gnome org>]

commit 2f103bc9480b6716ef6755e8b288188950059508
Author: Philip Withnall <withnall endlessm com>
Date:   Tue Apr 25 10:11:33 2017 +0100

    soup-message-headers: Add a missing (optional) annotation
    
    The total_length argument of soup_message_headers_get_content_range() is
    optional.
    
    Signed-off-by: Philip Withnall <withnall endlessm com>

 libsoup/soup-message-headers.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/libsoup/soup-message-headers.c b/libsoup/soup-message-headers.c
index 6ad554b..a180c6e 100644
--- a/libsoup/soup-message-headers.c
+++ b/libsoup/soup-message-headers.c
@@ -1171,8 +1171,8 @@ soup_message_headers_set_range (SoupMessageHeaders  *hdrs,
  * @hdrs: a #SoupMessageHeaders
  * @start: (out): return value for the start of the range
  * @end: (out): return value for the end of the range
- * @total_length: (out): return value for the total length of the resource,
- * or %NULL if you don't care.
+ * @total_length: (out) (optional): return value for the total length of the
+ * resource, or %NULL if you don't care.
  *
  * Parses @hdrs's Content-Range header and returns it in @start,
  * @end, and @total_length. If the total length field in the header