[tracker] Fixes NB#184882: tracker-extract is getting crashed for malformed gif files

[Aleksander Morgado <aleksm src gnome org>]

commit b7cab725447c531ad8b350dc26910932a45bbaf6
Author: Aleksander Morgado <aleksander lanedo com>
Date:   Mon Aug 16 09:38:12 2010 +0200

    Fixes NB#184882: tracker-extract is getting crashed for malformed gif files

 src/tracker-extract/tracker-extract-gif.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/src/tracker-extract/tracker-extract-gif.c b/src/tracker-extract/tracker-extract-gif.c
index 329c0ef..3028205 100644
--- a/src/tracker-extract/tracker-extract-gif.c
+++ b/src/tracker-extract/tracker-extract-gif.c
@@ -138,7 +138,8 @@ read_metadata (TrackerSparqlBuilder *preupdate,
 					return;
 				}
 #if defined(HAVE_EXEMPI)
-				if (strncmp(&ExtData[1],"XMP Data",8) == 0) {
+				if (ExtData &&
+				    strncmp(&ExtData[1],"XMP Data",8) == 0) {
 					while (ExtData != NULL && status == GIF_OK ) {
 						if ((status = DGifGetExtensionNext(gifFile, &ExtData)) == GIF_OK) {
 							if (ExtData != NULL) {