[gnote] remove a runtime warning caused by glib.

[Hubert Figuière <hub src gnome org>]

commit 50f953833de3c230731e83f33de1920fb5128281
Author: Hubert Figuiere <hub figuiere net>
Date:   Tue May 26 00:16:30 2009 -0400

    remove a runtime warning caused by glib.
---
 src/sharp/datetime.cpp |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/src/sharp/datetime.cpp b/src/sharp/datetime.cpp
index 994a7f6..82dadb8 100644
--- a/src/sharp/datetime.cpp
+++ b/src/sharp/datetime.cpp
@@ -108,6 +108,9 @@ namespace sharp {
   std::string DateTime::to_iso8601() const
   {
     std::string retval;
+    if(!is_valid()) {
+      return retval;
+    }
     char *  iso8601 = g_time_val_to_iso8601(const_cast<GTimeVal*>(&m_date));
     if(iso8601) {
       retval = iso8601;