[FIX] pos_restaurant: don't crash when printer have no url set

Have a printer in a pos.config that doesn't have a url set

Open the pos

Before this commit, there was a JS traceback, since we tried to call
string operation on undefined.

After this commit, we avoid the traceback with a behavior that *looks like* the v9.0's
i.e. we don't care if the url actually means something, we put a message in the console though

OPW 1858063

closes #25442

addons/pos_restaurant/static/src/js/multiprint.js

@@ -29,8 +29,10 @@ var Printer = core.Class.extend(mixins.PropertiesMixin,{
                 self.connection.rpc('/hw_proxy/print_xml_receipt',{receipt: r},{timeout: 5000})
                     .then(function(){
                         send_printing_job();
-                    },function(){
+                    },function(error, event){
                         self.receipt_queue.unshift(r);
+                        console.log('There was an error while trying to print the order:');
+                        console.log(error);
                     });
             }
         }
@@ -54,7 +56,7 @@ models.load_models({
 
         for(var i = 0; i < printers.length; i++){
             if(active_printers[printers[i].id]){
-                var url = printers[i].proxy_ip;
+                var url = printers[i].proxy_ip || '';
                 if(url.indexOf('//') < 0){
                     url = 'http://'+url;
                 }