[glib] docs: Clarify dest requirements of g_utf8_strncpy()

[Philip Withnall <pwithnall src gnome org>]

commit 1c0bed93a3f9a620d6d256799bb68d270145704d
Author: Patrick Griffis <tingping tingping se>
Date:   Tue Nov 28 06:43:56 2017 -0500

    docs: Clarify dest requirements of g_utf8_strncpy()
    
    (Minor wording tweak by Philip Withnall.)
    
    https://bugzilla.gnome.org/show_bug.cgi?id=520116

 glib/gutf8.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/glib/gutf8.c b/glib/gutf8.c
index ace4ee5..a0fb163 100644
--- a/glib/gutf8.c
+++ b/glib/gutf8.c
@@ -421,6 +421,9 @@ g_utf8_pointer_to_offset (const gchar *str,
  * must be valid UTF-8 encoded text. (Use g_utf8_validate() on all
  * text before trying to use UTF-8 utility functions with it.)
  * 
+ * Note you must ensure @dest is at least 4 * @n to fit the
+ * largest possible UTF-8 characters
+ *
  * Returns: @dest
  */
 gchar *