[FIX] pos_restaurant: fix customer deselection in the POS

The issue was that the deselection button did not appear when setting a
customer and then going back into the client list. Now new_client gets
reset whenever we hide the clientlist widget, which makes the hide/show
deselect button logic work.

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

@@ -966,7 +966,6 @@ var ClientListScreenWidget = ScreenWidget.extend({
         this.renderElement();
         this.details_visible = false;
         this.old_client = this.pos.get_order().get_client();
-        this.new_client = this.old_client;
 
         this.$('.back').click(function(){
             self.gui.back();
@@ -1016,6 +1015,10 @@ var ClientListScreenWidget = ScreenWidget.extend({
             self.clear_search();
         });
     },
+    hide: function () {
+        this._super();
+        this.new_client = null;
+    },
     barcode_client_action: function(code){
         if (this.editing_client) {
             this.$('.detail.barcode').val(code.code);
@@ -1058,7 +1061,7 @@ var ClientListScreenWidget = ScreenWidget.extend({
                 clientline = clientline.childNodes[1];
                 this.partner_cache.cache_node(partner.id,clientline);
             }
-            if( partners === this.new_client ){
+            if( partner === this.old_client ){
                 clientline.classList.add('highlight');
             }else{
                 clientline.classList.remove('highlight');