refactor: Improve BootGame error handling and thread initialization

- Add early validation for loader and title ID with critical error logging
- Move LoadROM call outside conditional block to always execute after validation
- Move emu_thread->start() to after all signal connections are established
- Improve code flow and organization for better maintainability

Signed-off-by: Zephyron <zephyron@citron-emu.org>

src/citron/main.cpp

@@ -2068,19 +2068,30 @@ void GMainWindow::BootGame(const QString& filename, Service::AM::FrontendAppletP
     last_filename_booted = filename;
 
     ConfigureFilesystemProvider(filename.toStdString());
+
     const auto v_file = Core::GetGameFileFromPath(vfs, filename.toUtf8().constData());
+
     const auto loader = Loader::GetLoader(*system, v_file, params.program_id, params.program_index);
 
-    if (loader != nullptr && loader->ReadProgramId(title_id) == Loader::ResultStatus::Success &&
+    if (loader == nullptr || loader->ReadProgramId(title_id) != Loader::ResultStatus::Success) {
-        type == StartGameType::Normal) {
+        // If we can't get a loader or read the title ID, we cannot proceed.
-        // Load per game settings
+        LOG_CRITICAL(Frontend, "Failed to load game: Could not determine title ID.");
+        return;
+    }
+
+    if (type == StartGameType::Normal) {
+        // Load per game settings if it is a normal boot
         const auto file_path =
             std::filesystem::path{Common::U16StringFromBuffer(filename.utf16(), filename.size())};
+
         const auto config_file_name = title_id == 0
                                           ? Common::FS::PathToUTF8String(file_path.filename())
                                           : fmt::format("{:016X}", title_id);
+
         QtConfig per_game_config(config_file_name, Config::ConfigType::PerGameConfig);
+
         system->HIDCore().ReloadInputDevices();
+
         system->ApplySettings();
 
         // Final Fantasy Tactics requires single-core mode to boot properly
@@ -2089,6 +2100,8 @@ void GMainWindow::BootGame(const QString& filename, Service::AM::FrontendAppletP
             Settings::values.use_multi_core.SetValue(false);
         }
 
+    }
+
     Settings::LogSettings();
 
     if (UISettings::values.select_user_on_boot && !user_flag_cmd_line) {
@@ -2098,30 +2111,30 @@ void GMainWindow::BootGame(const QString& filename, Service::AM::FrontendAppletP
             .display_options = {},
             .purpose = Service::AM::Frontend::UserSelectionPurpose::General,
         };
+
         if (SelectAndSetCurrentUser(parameters) == false) {
-                return;
+            return; // User cancelled profile selection
-            }
+        }
+
     }
 
-        // If the user specifies -u (successfully) on the cmd line, don't prompt for a user on first
-        // game startup only. If the user stops emulation and starts a new one, go back to the expected
-        // behavior of asking.
     user_flag_cmd_line = false;
 
+    // The core ROM loading logic. If this fails, we must not proceed.
     if (!LoadROM(filename, params)) {
         return;
     }
-    }
+
+    // This block is only reached if LoadROM returns true.
 
     system->SetShuttingDown(false);
     game_list->setDisabled(true);
 
     // Create and start the emulation thread
     emu_thread = std::make_unique<EmuThread>(*system);
-    emit EmulationStarting(emu_thread.get());
-    emu_thread->start();
 
-    // Register an ExecuteProgram callback such that Core can execute a sub-program
+    emit EmulationStarting(emu_thread.get());
+
     system->RegisterExecuteProgramCallback(
         [this](std::size_t program_index_) { render_window->ExecuteProgram(program_index_); });
 
@@ -2132,8 +2145,7 @@ void GMainWindow::BootGame(const QString& filename, Service::AM::FrontendAppletP
 
     connect(render_window, &GRenderWindow::Closed, this, &GMainWindow::OnStopGame);
     connect(render_window, &GRenderWindow::MouseActivity, this, &GMainWindow::OnMouseActivity);
-    // BlockingQueuedConnection is important here, it makes sure we've finished refreshing our views
+
-    // before the CPU continues
     connect(emu_thread.get(), &EmuThread::DebugModeEntered, waitTreeWidget,
             &WaitTreeWidget::OnDebugModeEntered, Qt::BlockingQueuedConnection);
     connect(emu_thread.get(), &EmuThread::DebugModeLeft, waitTreeWidget,
@@ -2142,6 +2154,9 @@ void GMainWindow::BootGame(const QString& filename, Service::AM::FrontendAppletP
     connect(emu_thread.get(), &EmuThread::LoadProgress, loading_screen,
             &LoadingScreen::OnLoadProgress, Qt::QueuedConnection);
 
+    // Start the thread AFTER all connections are set up
+    emu_thread->start();
+
     // Update the GUI
     UpdateStatusButtons();
     if (ui->action_Single_Window_Mode->isChecked()) {