[FIX] point_of_sale: correct remaining screen_selector calls

Deprecated in 9.0, to replace with gui.show_popup
Was crashing when displaying an error
opw-695106

addons/point_of_sale/static/src/js/devices.js

@@ -421,7 +421,7 @@ var ProxyDevice  = core.Class.extend(core.mixins.PropertiesMixin,{
                         send_printing_job();
                     },function(error){
                         if (error) {
-                            self.pos.chrome.screen_selector.show_popup('error-traceback',{
+                            self.pos.gui.show_popup('error-traceback',{
                                 'title': _t('Printing Error: ') + error.data.message,
                                 'body':  error.data.debug,
                             });

addons/point_of_sale/static/src/js/screens.js

@@ -1831,7 +1831,7 @@ var PaymentScreenWidget = ScreenWidget.extend({
         var plines = order.get_paymentlines();
         for (var i = 0; i < plines.length; i++) {
             if (plines[i].get_type() === 'bank' && plines[i].get_amount() < 0) {
-                this.pos_widget.screen_selector.show_popup('error',{
+                this.gui.show_popup('error',{
                     'message': _t('Negative Bank Payment'),
                     'comment': _t('You cannot have a negative amount in a Bank payment. Use a cash payment method to return money to the customer.'),
                 });