[epiphany] web-extension: Null-check before destroying sync service

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 7588e29a1373e8d13c0bcc616b6a3a877880d1fa
Author: Michael Catanzaro <mcatanzaro igalia com>
Date:   Tue Mar 27 10:05:13 2018 -0500

    web-extension: Null-check before destroying sync service
    
    https://bugzilla.gnome.org/show_bug.cgi?id=794728

 embed/web-extension/ephy-web-extension.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/embed/web-extension/ephy-web-extension.c b/embed/web-extension/ephy-web-extension.c
index 07127a7..95f1715 100644
--- a/embed/web-extension/ephy-web-extension.c
+++ b/embed/web-extension/ephy-web-extension.c
@@ -1589,7 +1589,7 @@ ephy_prefs_sync_user_cb (GSettings *settings,
    */
   if (ephy_sync_utils_user_is_signed_in ())
     ephy_web_extension_create_sync_service (extension);
-  else
+  else if (extension->sync_service)
     ephy_web_extension_destroy_sync_service (extension);
 }