[balsa] Return NULL string when date is zero

[Peter Bloomfield <PeterB src gnome org>]

commit 6eda4e7e9e51dcacd987f9ddd0f1cc9927b17554
Author: Peter Bloomfield <PeterBloomfield bellsouth net>
Date:   Wed Jul 7 08:42:09 2010 -0400

    Return NULL string when date is zero
    
    	* libbalsa/libbalsa.c (libbalsa_date_to_utf8): return NULL when
    	date is zero; fixes bug #623740 (Helmut Jarausch).

 ChangeLog           |    5 +++++
 libbalsa/libbalsa.c |    4 ++++
 2 files changed, 9 insertions(+), 0 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index 4880fc9..db67d7a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2010-07-07  Peter Bloomfield
+
+	* libbalsa/libbalsa.c (libbalsa_date_to_utf8): return NULL when
+	date is zero; fixes bug #623740 (Helmut Jarausch).
+
 2010-06-04  Peter Bloomfield
 
 	Drop legacy icon names.
diff --git a/libbalsa/libbalsa.c b/libbalsa/libbalsa.c
index 61cd7ff..1da42db 100644
--- a/libbalsa/libbalsa.c
+++ b/libbalsa/libbalsa.c
@@ -271,6 +271,10 @@ libbalsa_date_to_utf8(const time_t *date, const gchar *date_string)
     g_return_val_if_fail(date != NULL, NULL);
     g_return_val_if_fail(date_string != NULL, NULL);
 
+    if (!*date)
+        /* Missing "Date:" field?  It is required by RFC 2822. */
+        return NULL;
+
     localtime_r(date, &footime);
 
     strftime(rettime, sizeof(rettime), date_string, &footime);