[gimp] plug-ins: don't crash loading a transparent indexed png

[Massimo Valentini <mvalentini src gnome org>]

commit d3e68fc995066075686157a49a9fd5b67a77d5af
Author: Massimo Valentini <mvalentini src gnome org>
Date:   Mon Jul 9 18:04:08 2012 +0200

    plug-ins: don't crash loading a transparent indexed png
    
    with no text chunk, in that case 'i' == tile_height and
    
    *** glibc detected *** ...2.0/plug-ins/file-png:
      double free or corruption (out): 0x00000000011af590 ***

 plug-ins/common/file-png.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/plug-ins/common/file-png.c b/plug-ins/common/file-png.c
index e95d9fd..dc35885 100644
--- a/plug-ins/common/file-png.c
+++ b/plug-ins/common/file-png.c
@@ -1210,8 +1210,8 @@ load_image (const gchar  *filename,
 
           while (iter->length--)
             {
-              data[i * 2 + 1] = alpha[data[i * 2]];
-              data[i * 2] -= empty;
+              data[1] = alpha[data[0]];
+              data[0] -= empty;
 
               data += n_components;
             }