doc: Update changes.src

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
diff --git a/doc/changes.src b/doc/changes.src
index e27fade..75c355b 100644
--- a/doc/changes.src
+++ b/doc/changes.src
@@ -9,6 +9,9 @@
 
 \S{cl-2.09} Version 2.09
 
+\b Fixed NULL dereference if argument of \c{%strlen} resolves
+  to whitespace. For example if nonexistent macro parameter is used.
+
 \b \c{%ifenv}, \c{%elifenv}, \c{%ifnenv}, and \c{%elifnenv} directives
   introduced.  See \k{ifenv}.