Attempt to fix crash on switching printer (#14870)

# Description

attempt to fix #14851

# Screenshots/Recordings/Graphs

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## Tests

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src/slic3r/GUI/DeviceCore/DevManager.cpp

@@ -592,6 +592,7 @@ namespace Slic3r
         }
 
         selected_machine = dev_id;
+        record_user_last_machine(selected_machine);
         return true;
     }
 
@@ -854,21 +855,39 @@ namespace Slic3r
         }
     }
 
+    void DeviceManager::record_user_last_machine(const std::string& dev_id)
+    {
+        if (Slic3r::GUI::wxGetApp().app_config) {
+            Slic3r::GUI::wxGetApp().app_config->set("user_last_selected_machine", dev_id);
+        }
+    }
+
+    std::string DeviceManager::get_user_last_machine() const
+    {
+        if (Slic3r::GUI::wxGetApp().app_config) {
+            const auto& user_last_machine = Slic3r::GUI::wxGetApp().app_config->get("user_last_selected_machine");
+            if (!user_last_machine.empty()) {
+                return user_last_machine;
+            } else if (m_agent) {
+                return m_agent->get_user_selected_machine();
+            }
+        }
+
+        return "";
+    }
+
     void DeviceManager::load_last_machine()
     {
-        // Get all available machines, include cloud machines and lan machines that have access right
-        auto all_machines = get_my_machine_list();
-        if (all_machines.empty())
-            return;
-        
-        // Then connect to the machine we last selected if available
-        const std::string last_monitor_machine = m_agent ? m_agent->get_user_selected_machine() : "";
-        const auto        last_machine         = all_machines.find(last_monitor_machine);
-        if (last_machine != all_machines.end()) {
-            this->set_selected_machine(last_machine->second->get_dev_id());
+        if (userMachineList.empty()) return;
+        else if (userMachineList.size() == 1) {
+            this->set_selected_machine(userMachineList.begin()->second->get_dev_id());
         } else {
-            // If not, then select the first available one
-            this->set_selected_machine(all_machines.begin()->second->get_dev_id());
+            const auto& last_monitor_machine = get_user_last_machine();
+            if (userMachineList.find(last_monitor_machine) != userMachineList.end()) {
+                set_selected_machine(last_monitor_machine);
+            } else {
+                this->set_selected_machine(userMachineList.begin()->second->get_dev_id());
+            }
         }
     }
 

src/slic3r/GUI/DeviceCore/DevManager.h

@@ -48,6 +48,9 @@ public:
     MachineObject* get_selected_machine();
     bool set_selected_machine(std::string dev_id);
 
+    void record_user_last_machine(const std::string& dev_id);
+    std::string get_user_last_machine() const;
+
     // local machine
     void           set_local_selected_machine(std::string dev_id) { local_selected_machine = dev_id; };
     MachineObject* get_local_selected_machine() const { return get_local_machine(local_selected_machine); }

src/slic3r/GUI/GUI_App.cpp

@@ -2637,7 +2637,6 @@ void GUI_App::on_start_subscribe_again(std::string dev_id)
 
         if ( (dev_id == obj->get_dev_id()) && obj->is_connecting() && obj->subscribe_counter > 0) {
             obj->subscribe_counter--;
-            if(wxGetApp().getAgent()) wxGetApp().getAgent()->set_user_selected_machine(dev_id);
             BOOST_LOG_TRIVIAL(info) << __FUNCTION__ << ": dev_id=" << obj->get_dev_id();
         }
     });