[gnome-calendar] manager: prevent a segfault when opening edit dialog with no sources connected

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 17e5327cf467b0320b3836ecbb12e54a835b1c49
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Tue Jan 13 17:10:39 2015 -0200

    manager: prevent a segfault when opening edit dialog with no sources connected

 src/gcal-manager.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/src/gcal-manager.c b/src/gcal-manager.c
index 0bb7daf..ea04b66 100644
--- a/src/gcal-manager.c
+++ b/src/gcal-manager.c
@@ -934,6 +934,9 @@ gcal_manager_is_client_writable (GcalManager *manager,
   priv = gcal_manager_get_instance_private (manager);
   unit = g_hash_table_lookup (priv->clients, source);
 
+  if (unit == NULL)
+    return FALSE;
+
   return unit->connected && e_client_is_readonly (E_CLIENT (unit->client));
 }