[gnome-software] Fix a crash if a plugin emits status changed without an app set

[Richard Hughes <rhughes src gnome org>]

commit aba1586699e8bf973770efa4023d9eedca31ddaf
Author: Richard Hughes <richard hughsie com>
Date:   Fri Jun 30 10:03:36 2017 +0100

    Fix a crash if a plugin emits status changed without an app set

 src/gs-loading-page.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/src/gs-loading-page.c b/src/gs-loading-page.c
index 5a72491..03664ba 100644
--- a/src/gs-loading-page.c
+++ b/src/gs-loading-page.c
@@ -67,7 +67,8 @@ gs_loading_page_status_changed_cb (GsPluginLoader *plugin_loader,
 
        /* update label */
        if (status == GS_PLUGIN_STATUS_DOWNLOADING) {
-               str = gs_app_get_summary_missing (app);
+               if (app != NULL)
+                       str = gs_app_get_summary_missing (app);
                if (str == NULL) {
                        /* TRANSLATORS: initial start */
                        str = _("Software catalog is being downloaded");