Qt: Fix Big Picture UI locking up after game list switch

pcsx2-qt/QtHost.cpp

@@ -537,10 +537,6 @@ void EmuThread::setSurfaceless(bool surfaceless)
 	if (!MTGS::IsOpen() || m_is_surfaceless == surfaceless)
 		return;
 
-	// If we went surfaceless and were running the fullscreen UI, stop MTGS running idle.
-	// Otherwise, we'll keep trying to present to nothing.
-	MTGS::SetRunIdle(!surfaceless && m_run_fullscreen_ui);
-
 	// This will call back to us on the MTGS thread.
 	m_is_surfaceless = surfaceless;
 	MTGS::UpdateDisplayWindow();

pcsx2/GS/GS.cpp

@@ -508,6 +508,12 @@ void GSGameChanged()
 		GSTextureReplacements::GameChanged();
 }
 
+bool GSHasDisplayWindow()
+{
+	pxAssert(g_gs_device);
+	return (g_gs_device->GetWindowInfo().type != WindowInfo::Type::Surfaceless);
+}
+
 void GSResizeDisplayWindow(int width, int height, float scale)
 {
 	g_gs_device->ResizeWindow(width, height, scale);

pcsx2/GS/GS.h

@@ -96,6 +96,7 @@ void GSPresentCurrentFrame();
 void GSThrottlePresentation();
 void GSGameChanged();
 void GSSetDisplayAlignment(GSDisplayAlignment alignment);
+bool GSHasDisplayWindow();
 void GSResizeDisplayWindow(int width, int height, float scale);
 void GSUpdateDisplayWindow();
 void GSSetVSyncMode(VsyncMode mode);

pcsx2/MTGS.cpp

@@ -324,7 +324,7 @@ void MTGS::MainLoop()
 
 	while (true)
 	{
-		if (s_run_idle_flag.load(std::memory_order_acquire) && VMManager::GetState() != VMState::Running)
+		if (s_run_idle_flag.load(std::memory_order_acquire) && VMManager::GetState() != VMState::Running && GSHasDisplayWindow())
 		{
 			if (!s_sem_event.CheckForWork())
 			{