Fix: Missed return in ASSET_OT_bundle_install item enumerator

Discovered from inspection.

Differential Revision: https://developer.blender.org/D15699

source/blender/editors/asset/intern/asset_ops.cc

@@ -781,6 +781,7 @@ static const EnumPropertyItem *rna_asset_library_reference_itemf(bContext *UNUSE
   const EnumPropertyItem *items = ED_asset_library_reference_to_rna_enum_itemf(false);
   if (!items) {
     *r_free = false;
+    return nullptr;
   }
 
   *r_free = true;