[evolution-data-server] On The Web calendars don't work when the server doesn't return ETag header

[Milan Crha <mcrha src gnome org>]

commit ae9586ac8694f38beb9fd1562cd7ae2be32e6a61
Author: Milan Crha <mcrha redhat com>
Date:   Fri May 19 12:36:16 2017 +0200

    On The Web calendars don't work when the server doesn't return ETag header

 src/calendar/backends/http/e-cal-backend-http.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/calendar/backends/http/e-cal-backend-http.c b/src/calendar/backends/http/e-cal-backend-http.c
index a9e9b75..67b4cc5 100644
--- a/src/calendar/backends/http/e-cal-backend-http.c
+++ b/src/calendar/backends/http/e-cal-backend-http.c
@@ -309,7 +309,7 @@ ecb_http_get_changes_sync (ECalMetaBackend *meta_backend,
                new_etag = soup_message_headers_get_one (message->response_headers, "ETag");
                if (new_etag && !*new_etag) {
                        new_etag = NULL;
-               } else if (g_strcmp0 (last_sync_tag, new_etag) == 0) {
+               } else if (new_etag && g_strcmp0 (last_sync_tag, new_etag) == 0) {
                        /* Nothing changed */
                        g_object_unref (message);