Only add variant override permission if inventory enabled

The permission shoul not be needed if inventory is disabled, but it will
prevent importing into the inventory if somehow we try to import into
inventory with inventory disabled.

app/models/product_import/product_importer.rb

@@ -193,6 +193,8 @@ module ProductImport
         order('is_primary_producer ASC, name').
         map { |e| @editable_enterprises[e.name] = e.id }
 
+      return unless OpenFoodNetwork::FeatureToggle.enabled?(:inventory, @current_user.enterprises)
+
       @inventory_permissions = permissions.variant_override_enterprises_per_hub
     end