[IMP] stock: recompute state speedup

The recomputation of stock move state is often done with already
the correct state (for instance in the case of move line deletion only
one of the deletion will change the state).

This commit check the move state before changing it only when it's
necessary.

Task: 2507143
Part-of: odoo/odoo#78370
Co-authored-by: Remy Voet <ryv@odoo.com>