[evolution-data-server] e-source-registry-server: Fix a potential NULL pointer dereference

[Philip Withnall <pwithnall src gnome org>]

commit 3b90f87ebe6aa506cbd923a22ce1a39d57c85273
Author: Philip Withnall <philip tecnocode co uk>
Date:   Sat Nov 1 14:16:52 2014 +0000

    e-source-registry-server: Fix a potential NULL pointer dereference
    
    On the code path where backend is NULL, error is always NULL, so
    dereferencing error->message will result in a crash.
    
    Coverity issue: #1250457
    
    https://bugzilla.gnome.org/show_bug.cgi?id=739494

 libebackend/e-source-registry-server.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/libebackend/e-source-registry-server.c b/libebackend/e-source-registry-server.c
index 2e72304..7e82e52 100644
--- a/libebackend/e-source-registry-server.c
+++ b/libebackend/e-source-registry-server.c
@@ -1179,7 +1179,8 @@ source_registry_server_source_added (ESourceRegistryServer *server,
                } else {
                        g_warning (
                                "No collection backend '%s' for %s: %s",
-                               backend_name, e_source_get_uid (source), error->message);
+                               backend_name, e_source_get_uid (source),
+                               error ? error->message : "Unknown error");
 
                        g_clear_error (&error);
                }