[gnome-software: 1/3] Fix crash loading empty DEP-11 data.

[Philip Withnall <pwithnall src gnome org>]

commit aa9a87d65b143611ab4201f885e4bafcb4147a8f
Author: Robert Ancell <robert ancell canonical com>
Date:   Mon May 24 12:43:59 2021 +1200

    Fix crash loading empty DEP-11 data.
    
    as_metadata_components_to_collection returns NULL if there is nothing to serialize, and also if an error 
occurs.
    Add a check to detect the former case instead of attempting to read an unset GError.

 plugins/core/gs-plugin-appstream.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)
---
diff --git a/plugins/core/gs-plugin-appstream.c b/plugins/core/gs-plugin-appstream.c
index e353fa45e..a013711c0 100644
--- a/plugins/core/gs-plugin-appstream.c
+++ b/plugins/core/gs-plugin-appstream.c
@@ -346,9 +346,16 @@ gs_plugin_appstream_load_dep11_cb (XbBuilderSource *self,
                return NULL;
        }
 
-       xml = as_metadata_components_to_collection (mdata, AS_FORMAT_KIND_XML, error);
-       if (xml == NULL)
-               return NULL;
+       xml = as_metadata_components_to_collection (mdata, AS_FORMAT_KIND_XML, &tmp_error);
+       if (xml == NULL) {
+               if (tmp_error != NULL) {
+                       g_propagate_error (error, g_steal_pointer (&tmp_error));
+                       return NULL;
+               }
+
+               xml = g_strdup("");
+       }
+
        return g_memory_input_stream_new_from_data (g_steal_pointer (&xml), -1, g_free);
 }