[libpng16] Updated description of filler-byte bugfix in CHANGES.

ANNOUNCE

-Libpng 1.6.19beta03 - September 18, 2015
+Libpng 1.6.19beta03 - September 19, 2015
 
 This is not intended to be a public release.  It will be replaced
 within a few weeks by a public version or by another test version.

CHANGES

@@ -5145,7 +5145,9 @@ Version 1.6.17beta01 [January 29, 2015]
   Added testing of png_set_packing() to pngvalid.c
   Regenerated configure scripts in the *.tar distributions with libtool-2.4.4
   Implement previously untested cases of libpng transforms in pngvalid.c
-  Fixed byte order in 2-byte filler, in png_do_read_filler().
+  Fixed byte order in png_do_read_filler() with 16-bit input. Previously
+    the high and low bytes of the filler, from png_set_filler() or from
+    png_set_add_alpha(), were read in the wrong order.
   Made the check for out-of-range values in png_set_tRNS() detect
     values that are exactly 2^bit_depth, and work on 16-bit platforms.
   Merged some parts of libpng-1.6.17beta01 and libpng-1.7.0beta47.
@@ -5345,7 +5347,7 @@ Version 1.6.19beta02 [August 19, 2015]
     in ANSI-C (unlike 0x80000000 in the signed case) the checking that
     occurs later can catch them (John Bowler).
 
-Version 1.6.19beta03 [September 18, 2015]
+Version 1.6.19beta03 [September 19, 2015]
   Fixed png_save_int_32 when int is not 2's complement (John Bowler).
   Updated libpng16 with all the recent test changes from libpng17,
     including changes to pngvalid.c to ensure that the original,