In the case of draft pickings/MOs, the reception_report_main
component's "Assign All" button was NOT disabled, which could result
in an IndexError if the button was pushed. Note that this issue does not
occur for the "Assign All" button within a table because the button is
correctly not shown at all when there are no assignable lines within it.

Noticed during task: 3046178

Part-of: odoo/odoo#119954