[FIX] sale_timesheet: fix traceback while set empty in timesheet notebook

Steps to reproduce:
-------------------------
- Install project and sale_timesheet module
- Open the Project module
- Go to task's timesheet notebook
- Add a new line
- Set empty in so_line field, raises traceback

Issue:
--------
- In timesheet notebook, when we set so_line as an empty .it will raises
  traceback.

Cause:
---------
- #145821 when set empty so_line field there is undefined value read.

Fix:
-------
- On a field change, compare the so_line field value with proper record id check
  with new value.

task-3642371

closes odoo/odoo#147546

X-original-commit: ed2417225975001dd7b6ec1d3655fe880fe2c108
Signed-off-by: Xavier Bol (xbo) <xbo@odoo.com>

addons/sale_timesheet/static/src/components/so_line_field/so_line_field.js

@@ -13,7 +13,7 @@ export class SoLineField extends Many2OneField {
             update(value, params);
             if ( // field is unset AND the old & new so_lines are different
                 !this.props.record.data.is_so_line_edited &&
-                this.props.value[0] != (value[0] && value[0].id)
+                this.value[0] != value[0]?.id
             ) {
                 this.props.record.update({ is_so_line_edited: true });
             }