[gthumb] Revert earlier change, don't assert fd is not null before unref

[Michael J. Chudobiak <mjc src gnome org>]

commit 59ac23d348820cce8966c5ba584194ce9211d14f
Author: Michael J. Chudobiak <mjc avtechpulse com>
Date:   Fri May 1 12:27:34 2009 -0400

    Revert earlier change, don't assert fd is not null before unref
---
 libgthumb/file-data.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/libgthumb/file-data.c b/libgthumb/file-data.c
index 76a3fae..3dbc5cb 100644
--- a/libgthumb/file-data.c
+++ b/libgthumb/file-data.c
@@ -173,7 +173,8 @@ file_data_dup (FileData *source)
 void
 file_data_unref (FileData *fd)
 {
-	g_return_if_fail (fd != NULL);	
+	if (fd == NULL)
+		return;
 
 	fd->ref--;