[gnome-software] trivial: Fix critical warning for broken shell extensions

[Richard Hughes <rhughes src gnome org>]

commit 07a2725cf66228e80abbf4070e5b66113feaf0a8
Author: Richard Hughes <richard hughsie com>
Date:   Mon Jun 27 11:48:10 2016 +0100

    trivial: Fix critical warning for broken shell extensions

 src/plugins/gs-plugin-shell-extensions.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/plugins/gs-plugin-shell-extensions.c b/src/plugins/gs-plugin-shell-extensions.c
index 61dff42..68545f7 100644
--- a/src/plugins/gs-plugin-shell-extensions.c
+++ b/src/plugins/gs-plugin-shell-extensions.c
@@ -353,7 +353,7 @@ gs_plugin_refine_app (GsPlugin *plugin,
 
        /* can we get the AppStream-created app state using the cache */
        uuid = gs_app_get_metadata_item (app, "shell-extensions::uuid");
-       if (gs_app_get_state (app) == AS_APP_STATE_UNKNOWN) {
+       if (uuid != NULL && gs_app_get_state (app) == AS_APP_STATE_UNKNOWN) {
                GsApp *app_cache = gs_plugin_cache_lookup (plugin, uuid);
                if (app_cache != NULL) {
                        g_debug ("copy cached state for %s",