[tracker] Fix GStreamer extractor, genre can be NULL too

[Philip Van Hoof <pvanhoof src gnome org>]

commit 9fb85028d41dba04a95375db55ef32f450f2b4d2
Author: Philip Van Hoof <philip codeminded be>
Date:   Mon Dec 13 14:27:48 2010 +0100

    Fix GStreamer extractor, genre can be NULL too

 src/tracker-extract/tracker-extract-gstreamer.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/tracker-extract/tracker-extract-gstreamer.c b/src/tracker-extract/tracker-extract-gstreamer.c
index cd36824..2e92e3a 100644
--- a/src/tracker-extract/tracker-extract-gstreamer.c
+++ b/src/tracker-extract/tracker-extract-gstreamer.c
@@ -753,7 +753,7 @@ extract_metadata (MetadataExtractor      *extractor,
 		}
 
 		gst_tag_list_get_string (extractor->tagcache, GST_TAG_GENRE, &genre);
-		if (g_strcmp0 (genre, "Unknown") != 0) {
+		if (genre && g_strcmp0 (genre, "Unknown") != 0) {
 			tracker_sparql_builder_predicate (metadata, "nfo:genre");
 			tracker_sparql_builder_object_unvalidated (metadata, genre);
 		}