[easytag] Improve const use in FLAC and Ogg tagging

[David King <davidk src gnome org>]

commit b99d6c73f170524aec7f175c6f278b72639ff3bd
Author: David King <amigadave amigadave com>
Date:   Wed May 25 20:53:54 2016 +0200

    Improve const use in FLAC and Ogg tagging

 src/tags/flac_tag.c |    6 +++++-
 src/tags/ogg_tag.c  |    2 +-
 2 files changed, 6 insertions(+), 2 deletions(-)
---
diff --git a/src/tags/flac_tag.c b/src/tags/flac_tag.c
index e811753..1b02e29 100644
--- a/src/tags/flac_tag.c
+++ b/src/tags/flac_tag.c
@@ -618,6 +618,8 @@ vc_block_append_other_tag (FLAC__StreamMetadata *vc_block,
     field.entry = (FLAC__byte *)tag;
     field.length = strlen (tag);
 
+    /* Safe to pass const data, if the last argument (copy) is true, according
+     * to the FLAC API reference. */
     if (!FLAC__metadata_object_vorbiscomment_append_comment (vc_block, field,
                                                              true))
     {
@@ -1029,10 +1031,12 @@ flac_tag_write_file_tag (const ET_File *ETFile,
 
                 /* Picture data. */
                 data = g_bytes_get_data (pic->bytes, &data_size);
+                /* Safe to pass const data, if the last argument (copy) is
+                 * TRUE, according the the FLAC API reference. */
                 FLAC__metadata_object_picture_set_data (picture_block,
                                                         (FLAC__byte *)data,
                                                         (FLAC__uint32)data_size,
-                                                        TRUE);
+                                                        true);
                 
                 if (!FLAC__metadata_object_picture_is_legal (picture_block,
                                                              &violation))
diff --git a/src/tags/ogg_tag.c b/src/tags/ogg_tag.c
index 0bf751c..7856e74 100644
--- a/src/tags/ogg_tag.c
+++ b/src/tags/ogg_tag.c
@@ -1096,7 +1096,7 @@ ogg_tag_write_file_tag (const ET_File *ETFile,
         /* Adding MIME string and its length. */
         convert_to_byte_array (strlen (mime), array);
         add_to_guchar_str (ustring, &ustring_len, array, 4);
-        add_to_guchar_str (ustring, &ustring_len, (guchar *)mime,
+        add_to_guchar_str (ustring, &ustring_len, (const guchar *)mime,
                            strlen (mime));
 
         /* Adding picture description. */