[evolution-ews] Avoid crash on receiving component with empty TZID=

[David Woodhouse <dwmw2 src gnome org>]

commit c476d695547f7988caceb43387d9ee4117661c00
Author: David Woodhouse <David Woodhouse intel com>
Date:   Wed Jul 20 22:57:51 2011 -0700

    Avoid crash on receiving component with empty TZID=
    
    Not entirely sure how best to cope with this, but crashing certainly isn't
    the answer.

 src/calendar/e-cal-backend-ews.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/src/calendar/e-cal-backend-ews.c b/src/calendar/e-cal-backend-ews.c
index df1daa0..d688366 100644
--- a/src/calendar/e-cal-backend-ews.c
+++ b/src/calendar/e-cal-backend-ews.c
@@ -2664,7 +2664,8 @@ add_item_to_cache (ECalBackendEws *cbews, EEwsItem *item, gchar *uid)
 		if (vtimezone) {
 			zone = icaltimezone_new ();
 			icaltimezone_set_component (zone, icalcomponent_new_clone (vtimezone));
-			e_cal_backend_store_put_timezone (priv->store, zone);
+			if (icaltimezone_get_tzid(zone))
+				e_cal_backend_store_put_timezone (priv->store, zone);
 
 			icaltimezone_free (zone, TRUE);
 		}