[gnome-software] trivial: Add some debugging to help fix an issue

[Richard Hughes <rhughes src gnome org>]

commit dafb4cf81283c76040d28af7ecb9a77ea8da600c
Author: Richard Hughes <richard hughsie com>
Date:   Thu Feb 18 14:37:01 2016 +0000

    trivial: Add some debugging to help fix an issue

 src/plugins/gs-plugin-xdg-app.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/src/plugins/gs-plugin-xdg-app.c b/src/plugins/gs-plugin-xdg-app.c
index 08c544d..211cb26 100644
--- a/src/plugins/gs-plugin-xdg-app.c
+++ b/src/plugins/gs-plugin-xdg-app.c
@@ -842,8 +842,11 @@ gs_plugin_refine_item_metadata (GsPlugin *plugin,
 
        /* parse the ref */
        xref = xdg_app_ref_parse (gs_app_get_source_default (app), error);
-       if (xref == NULL)
+       if (xref == NULL) {
+               g_prefix_error (error, "failed to parse '%s': ",
+                               gs_app_get_source_default (app));
                return FALSE;
+       }
        gs_plugin_xdg_app_set_metadata (app, xref);
 
        /* success */