[devel] Avoid a possible NULL dereference in debug builds

in png_set_text-2().  Bug discovered by Evan Rouault, using cochinelle.
diff --git a/CHANGES b/CHANGES
index fd1cab9..18a39bc 100644
--- a/CHANGES
+++ b/CHANGES
@@ -2189,7 +2189,8 @@
   Fixed up xcode project (Alam Arias)
   Added a prototype for png_64bit_product() in png.c
 
-version 1.4.0beta70 [July 25, 2009]
+version 1.4.0beta70 [July 28, 2009]
+  Avoid a possible NULL dereference in debug build, in png_set_text_2().
 
 version 1.4.0betaN [future]
   Build shared libraries with -lz and sometimes -lm.