### Steps to reproduce:
- Install `sale_subscription_timesheet` module
- Create a subscription (Order A) with delivered-timesheet products and log timesheets within its current period (e.g., January)
- Create a standard order (Order B) with delivered-timesheet products and log timesheets outside of Order A's period (e.g., March)
- Select both orders and invoice them simultaneously in a single batch (uncheck 'Consolidated Billing')
> Result: Order B's invoice is created but silently fails to link its March timesheets, because they fall outside Order A's January window.

### Cause of Issue:
In `_link_timesheets_to_invoice`, the `start_date` and `end_date` parameters are overwritten inside the invoice line loop when `_get_range_dates` is called. Because these variables are never reset per iteration, the first order that yields a date range locks in that window for every subsequent invoice line in the batch. Timesheets outside this leaked window are silently ignored.

Additionally, the `_get_range_dates` hook is invoked before verifying if the invoice line actually contains timesheet products, causing it to execute on empty recordsets (e.g. invoice line notes)

### Fix:
Prevent the date range leak by preserving the original parameter state of the dates and safely ensure the extension hook is never invoked with an empty recordset.

opw-6507110

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Forward-Port-Of: odoo/odoo#284781