Tweak new BKE_id_is_in_global_main to accept NULL pointer (and consider them as valid).

source/blender/blenkernel/intern/library.c

@@ -2418,6 +2418,7 @@ void BKE_id_tag_clear_atomic(ID *id, int tag)
 /** Check that given ID pointer actually is in G_MAIN.
  * Main intended use is for debug asserts in places we cannot easily get rid of G_Main... */
 bool BKE_id_is_in_gobal_main(ID *id) {
-	return (BLI_findindex(which_libbase(G_MAIN, GS(id->name)), id) != -1);
+	/* We do not want to fail when id is NULL here, even though this is a bit strange behavior... */
+	return (id == NULL || BLI_findindex(which_libbase(G_MAIN, GS(id->name)), id) != -1);
 }