[tracker/tracker-0.6] MetadataValue can be empty, avoid critical warnings when trying to retrieve it.

[Carlos Garnacho <carlosg src gnome org>]

commit 5cfa44bb3a12b75f04c0aec86ef0beb60b6c8616
Author: Carlos Garnacho <carlosg gnome org>
Date:   Fri May 22 15:11:04 2009 +0200

    MetadataValue can be empty, avoid critical warnings when trying to retrieve it.
---
 src/libtracker-data/tracker-data-query.c |   10 +++++++---
 1 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/src/libtracker-data/tracker-data-query.c b/src/libtracker-data/tracker-data-query.c
index 48f6cb3..ebfcbfd 100644
--- a/src/libtracker-data/tracker-data-query.c
+++ b/src/libtracker-data/tracker-data-query.c
@@ -609,10 +609,14 @@ db_get_metadata (TrackerService *service,
 
 		while (valid) {
 			tracker_db_result_set_get (result_set, 0, &str, -1);
-			result = g_string_append (result, str);
-			result = g_string_append (result, " ");
+
+			if (str) {
+				result = g_string_append (result, str);
+				result = g_string_append (result, " ");
+				g_free (str);
+			}
+
 			valid = tracker_db_result_set_iter_next (result_set);
-			g_free (str);
 		}
 
 		g_object_unref (result_set);