[tracker] tracker-extract: Fix crash in albumart support

[Jürg Billeter <juergbi src gnome org>]

commit f7ea6435e44eac22ba1b08ff1b12498c57daa872
Author: Jürg Billeter <j bitron ch>
Date:   Fri Jan 28 15:12:42 2011 +0100

    tracker-extract: Fix crash in albumart support
    
    Fixes NB#223148.

 src/tracker-extract/tracker-albumart.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)
---
diff --git a/src/tracker-extract/tracker-albumart.c b/src/tracker-extract/tracker-albumart.c
index 71c57db..e0c7cc2 100644
--- a/src/tracker-extract/tracker-albumart.c
+++ b/src/tracker-extract/tracker-albumart.c
@@ -567,7 +567,11 @@ albumart_request_download (TrackerStorage *storage,
 		                        ALBUMARTER_PATH,
 		                        ALBUMARTER_INTERFACE,
 		                        "Queue",
-		                        g_variant_new ("(sssu)", artist, album, "album", 0),
+		                        g_variant_new ("(sssu)",
+		                                       artist ? artist : "",
+		                                       album ? album : "",
+		                                       "album",
+		                                       0),
 		                        NULL,
 		                        G_DBUS_CALL_FLAGS_NONE,
 		                        -1,