[gnome-builder] flatpak: ensure we always have an arch to work with

[Christian Hergert <chergert src gnome org>]

commit 86433d60c4fc1de89f04c7d4a8e13f312fa0edfc
Author: Christian Hergert <chergert redhat com>
Date:   Fri Apr 30 13:51:36 2021 -0700

    flatpak: ensure we always have an arch to work with

 src/plugins/flatpak/gbp-flatpak-application-addin.c | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/src/plugins/flatpak/gbp-flatpak-application-addin.c 
b/src/plugins/flatpak/gbp-flatpak-application-addin.c
index 8400a8e9b..deac241ef 100644
--- a/src/plugins/flatpak/gbp-flatpak-application-addin.c
+++ b/src/plugins/flatpak/gbp-flatpak-application-addin.c
@@ -1555,6 +1555,9 @@ gbp_flatpak_application_addin_resolve_extension (GbpFlatpakApplicationAddin *sel
   if (!gbp_flatpak_split_id (sdk, &sdk_id, &sdk_arch, &sdk_branch))
     IDE_RETURN (NULL);
 
+  if (sdk_arch == NULL)
+    sdk_arch = g_strdup (flatpak_get_default_arch ());
+
   strings = g_string_chunk_new (4096);
   installations = g_ptr_array_ref (self->installations);