[tracker] tracker-extract-png: Insert "nfo:image-category-screenshot" as a URI

[Debarshi Ray <debarshir src gnome org>]

commit a5476d2221666e21c9e4f331a9aad662bd12acd0
Author: Debarshi Ray <debarshir gnome org>
Date:   Tue Jan 31 11:40:41 2017 +0100

    tracker-extract-png: Insert "nfo:image-category-screenshot" as a URI
    
    This is not a string, but a builtin class, so it must be dealt with as
    a URI.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=776723

 src/tracker-extract/tracker-extract-png.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/tracker-extract/tracker-extract-png.c b/src/tracker-extract/tracker-extract-png.c
index d77dc9e..fcfd5f4 100644
--- a/src/tracker-extract/tracker-extract-png.c
+++ b/src/tracker-extract/tracker-extract-png.c
@@ -562,7 +562,7 @@ read_metadata (TrackerResource      *metadata,
        g_ptr_array_free (keywords, TRUE);
 
        if (g_strcmp0(pd.software, "gnome-screenshot") == 0) {
-               tracker_resource_set_string (metadata, "nie:isPartOf", "nfo:image-category-screenshot");
+               tracker_resource_add_uri (metadata, "nie:isPartOf", "nfo:image-category-screenshot");
        }
 
        tracker_exif_free (ed);