Before this commit if we go to website and choose tasks and if we search
anything it shows no tasks available and if we select milestone it shows table.

Steps:
- Go to website and select tasks and search anything in search bar.
- Showing  no tasks available
- choose milestone from drop-down and search anything it will show table labels.

Fix:
- Added condition for checking if milestone is passing empty record set  and
 added another condition to handle it

task-3183771

closes odoo/odoo#114407

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