[FIX] mrp: produce wizard negative reserved qty

Usecase to reproduce:
BOM 1 product final F -> 2 components C
- 1 units of C in stock
- MO of 2 units of F
- Reserve MO
- Produce wizard 2 units of F -> C 4 to consume 1 reserved
- Update quantity to 1

-> The produce line for C contains -1 reserved

It happens because the system remove the quantity to consume on
the reservation. However sometimes the quantity reserved is lower
than the quantity to consume and it will result in a negative quantity
reserved.

addons/mrp/models/mrp_abstract_workorder.py

@@ -75,10 +75,11 @@ class MrpAbstractWorkorder(models.AbstractModel):
                             line_values['to_delete'] = workorder_line
                     else:
                         new_val = workorder_line.qty_to_consume - qty_todo
+                        new_reserved = max(0, workorder_line.qty_reserved - qty_todo)
                         line_values['to_update'][workorder_line] = {
                             'qty_to_consume': new_val,
                             'qty_done': new_val,
-                            'qty_reserved': new_val,
+                            'qty_reserved': new_reserved,
                         }
                         qty_todo = 0
             else: