Fix T93431: Crash when empty is marked as asset

Make `ED_preview_id_is_supported(ID *)` NULL-safe. It's semantically
valid, as it's not possible to render a preview of a NULL ID.

The crash was introduced in 481f032f5c

Reviewed By: sybren, jbakker

Maniphest Tasks: T93431

Differential Revision: https://developer.blender.org/D13398

source/blender/editors/render/render_preview.c

@@ -1764,6 +1764,10 @@ static void icon_preview_free(void *customdata)
  */
 bool ED_preview_id_is_supported(const ID *id)
 {
+  if (id == NULL) {
+    return false;
+  }
+
   if (GS(id->name) == ID_OB) {
     return object_preview_is_type_supported((const Object *)id);
   }