[gimp] plug-ins: fix #6871 indexed tga file cannot be saved

[Jacob Boerema <jboerema src gnome org>]

commit 059599fc78058dd2a964d0ff05e830638cc89202
Author: Jacob Boerema <jgboerema gmail com>
Date:   Tue Jan 18 14:57:35 2022 -0500

    plug-ins: fix #6871 indexed tga file cannot be saved
    
    Exporting an image to TGA fails with a crash when it's an indexed image
    with alpha channel. We were not taking into account that even though
    the output is 1 byte per pixel, the input should allocate memory for
    2 bytes per pixel (1 color index and 1 alpha channel).

 plug-ins/common/file-tga.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/plug-ins/common/file-tga.c b/plug-ins/common/file-tga.c
index 8a74ecc51e..7c2e7e1a7b 100644
--- a/plug-ins/common/file-tga.c
+++ b/plug-ins/common/file-tga.c
@@ -1353,7 +1353,10 @@ save_image (GFile         *file,
       fputc (0, fp);
     }
 
-  pixels = g_new (guchar, width * out_bpp);
+  if (dtype == GIMP_INDEXEDA_IMAGE)
+    pixels = g_new (guchar, width * 2);
+  else
+    pixels = g_new (guchar, width * out_bpp);
   data   = g_new (guchar, width * out_bpp);
 
   for (row = 0; row < height; ++row)