[FIX] project: display title instead of empty block

Steps:
- Open Website > My Account > Projects
- Open the project in which the customer is not set
- Now perform 'group by customer' on that project.

Issue:
- A blank line is shown below the header line.

Cause:
- No condition is applied to it when we do not have a customer set.

Fix:
- Adding condition to display 'No Customer' instead of an empty block.

closes odoo/odoo#132149

Task: 3461563
Signed-off-by: Xavier Bol (xbo) <xbo@odoo.com>