Product availability cannot override staff availability in v4.14.8

To reproduce: Create a staff member and set him as available from 9:00 to 10:00 and from 12:00 to 14:00. Then set the product duration to 4 hours, assign the staff member, and create a product availability rule for 10:00 to 12:00 as AVAILABLE with priority -100. There will be no slots left but there should be.