[gnome-builder] podman: check for non-NULL layer

[Christian Hergert <chergert src gnome org>]

commit 5dd6b00b27b43a6ba019b3c9cfb4cf43f0b9c2bf
Author: Christian Hergert <chergert redhat com>
Date:   Wed Jan 26 08:56:46 2022 -0800

    podman: check for non-NULL layer

 src/plugins/podman/gbp-podman-runtime.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)
---
diff --git a/src/plugins/podman/gbp-podman-runtime.c b/src/plugins/podman/gbp-podman-runtime.c
index 896fbe9d1..9b4139095 100644
--- a/src/plugins/podman/gbp-podman-runtime.c
+++ b/src/plugins/podman/gbp-podman-runtime.c
@@ -273,10 +273,14 @@ resolve_overlay (GbpPodmanRuntime *runtime)
     }
 
   json_parser_load_from_file (parser, layer_json, NULL);
-  /* apply all parent layers */
-  do {
-    runtime->layers = g_list_append (runtime->layers, layer);
-  } while ((layer = find_parent_layer (runtime, parser, layer)));
+
+  if (layer != NULL)
+    {
+      /* apply all parent layers */
+      do {
+        runtime->layers = g_list_append (runtime->layers, layer);
+      } while ((layer = find_parent_layer (runtime, parser, layer)));
+    }
 
   /* apply image layer */
   json_parser_load_from_file (image_parser, image_json, NULL);