Description of problem:
Since 6.14 an error message is shown when you try to add a Product with no repos to a Sync Plan, but the product is added regardless the message.

Version-Release number of selected component (if applicable):
6.14.0 snap 14

How reproducible:
always

Steps to Reproduce:
1. Create a custom Product without any repo.
2. Create a Sync Plan.
3. Add the Product to the Sync Plan.

Actual results:
Error message "Cannot add product <prod> because it is disabled." is shown, but the product is added anyway.

Expected results:
Product is not added.