[easytag] Write Vorbis artwork with a depth per sample of 8

[David King <davidk src gnome org>]

commit cac75c6d565cf7c54d72775216010e3698c11af1
Author: David King <amigadave amigadave com>
Date:   Sun Mar 5 18:25:12 2017 +0000

    Write Vorbis artwork with a depth per sample of 8
    
    https://bugzilla.gnome.org/show_bug.cgi?id=779622

 src/tags/ogg_tag.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/src/tags/ogg_tag.c b/src/tags/ogg_tag.c
index 7856e74..f9ad0fd 100644
--- a/src/tags/ogg_tag.c
+++ b/src/tags/ogg_tag.c
@@ -1113,9 +1113,11 @@ ogg_tag_write_file_tag (const ET_File *ETFile,
         convert_to_byte_array (pic->height, array);
         add_to_guchar_str (ustring, &ustring_len, array, 4);
 
-        convert_to_byte_array (0, array);
+        /* GdkPicbuf only supports images with 8 bits per sample. */
+        convert_to_byte_array (8, array);
         add_to_guchar_str (ustring, &ustring_len, array, 4);
 
+        /* Non-indexed images should set this to zero. */
         convert_to_byte_array (0, array);
         add_to_guchar_str (ustring, &ustring_len, array, 4);