[FIX] stock: Don't set DO to ready if a move is empty

A stock move with 0 qty in initial demand is considered as 'ready'. But
those stock moves should be excluded of the picking state computation to
not false the readiness of the picking, especially if the delivery
policy is set to 'direct'.

opw-2611018

closes odoo/odoo#75194

Signed-off-by: William Henrotin <Whenrow@users.noreply.github.com>