[FIX] mrp_account, sale_mrp: check if BoM line is correct

Suppose an automated AVCO product category. When confirming an invoice,
if the associated product was a kit and if its BoM has changed during
the process, a traceback can occur.

To reproduce the issue:
(Need sale_management)
1. Create a product category PC:
    - Costing Method: AVCO
    - Inventory Valuation: Automated
2. Create 3 products P1, P2, P3:
    - Product Type: Storable
    - Category: PC
3. Update P3's quantity > 0
4. Create two bills of materials:
    - BOM01:
        - Product: P1
        - BoM Type: Kit
        - Components: 1 x P2
    - BOM02:
        - Product: P2
        - BoM Type: Kit
        - Components: 1 x P3
5. Create a sale order SO with 1 x P1
6. Confirm SO and process the delivery
7. Edit BOM02:
    - BoM Type: Manufacture
8. On SO, create the invoice INV
9. Confirm INV

Error: an Odoo Server Error is displayed with a traceback: "[...] in
_compute_average_price, bom_line_data = bom_lines[bom_line] [...]
KeyError: mrp.bom.line(19,)"

On step 7, when changing the BoM type, a new BoM line is created.
Therefore, in `_compute_average_price`, the BoM associated to the move
(i.e., `bom_line`) is not one of the lines in `bom_lines` (i.e., the new
BoM lines). There is already a check in case the line has been deleted,
but not if it has been changed.

OPW-2610685

closes odoo/odoo#78917

Signed-off-by: William Henrotin (whe) <whe@odoo.com>