Product capacity doesn't work

[Valentina R]

To reproduce:

Make an appointment with capacity 3 and assign 3 staff members and set availability every day from 08:00 to 20:00. Each staff member has capacity 1 and no availability rules.

Now when I book staff1 on Monday at 08:00, I can't book other staff members (staff2 and staff3).

First spotted this in 3.1.2, but maybe has been there longer.

[Željan Topić]

Fixed with 3.1.5