[FIX] account: Check Move Status Before Posting

Beforehand, if two users independently opened a draft
invoice on their respective sessions, then both of them
clicked on the "Post" button, then the invoice was
posted twice.
On a more general aspect, the view currently "prevents" users
from posting moves several times, but technically speaking,
nothing stops users from posting moves several times.

Now, after checking that the user indeed has the right to post
a move, the next check is about verifying that the move is
not already posted.

opw-2479201

closes odoo/odoo#68837

X-original-commit: 71b82693
Related: odoo/enterprise#17511
Signed-off-by: oco-odoo <oco-odoo@users.noreply.github.com>
Signed-off-by: Julien CHEVREAU <Julien-CHEVREAU@users.noreply.github.com>