hr_timesheet_invoice: Permit modification of invoiced timesheet lines

The existing code wouldn't even permit to remove the invoice association
in case the invoice is cancelled...

addons/hr_timesheet_invoice/hr_timesheet_invoice.py

@@ -126,7 +126,7 @@ class account_analytic_line(osv.osv):
     }
 
     def write(self, cr, uid, ids, vals, context=None):
-        self._check_inv(cr, uid, ids, vals)
+        #self._check_inv(cr, uid, ids, vals)
         return super(account_analytic_line,self).write(cr, uid, ids, vals,
                 context=context)