[gnome-builder] flatpak: Set error before returning NULL

[Matthew Leeds <mwleeds src gnome org>]

commit e9513c21fc42e8969bbe1e0e62b8c4cf9f044984
Author: Matthew Leeds <mleeds redhat com>
Date:   Thu Dec 29 18:50:19 2016 -0600

    flatpak: Set error before returning NULL

 plugins/flatpak/gbp-flatpak-clone-widget.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)
---
diff --git a/plugins/flatpak/gbp-flatpak-clone-widget.c b/plugins/flatpak/gbp-flatpak-clone-widget.c
index 9129ceb..0134738 100644
--- a/plugins/flatpak/gbp-flatpak-clone-widget.c
+++ b/plugins/flatpak/gbp-flatpak-clone-widget.c
@@ -477,7 +477,14 @@ get_source (GbpFlatpakCloneWidget  *self,
     self->id = g_strdup (json_object_get_string_member (root_object, "id"));
 
   if (self->id == NULL)
-    return NULL;
+    {
+      g_set_error (error,
+                   G_IO_ERROR,
+                   G_IO_ERROR_INVALID_DATA,
+                   "No app-id set in flatpak manifest %s",
+                   self->manifest);
+      return NULL;
+    }
 
   modules = json_object_get_array_member (root_object, "modules");
   num_modules = json_array_get_length (modules);