Fix a couple race conditions.

Checks if another game is already starting to boot before starting to boot a new one, and only change video backend, and dual core if a game is actually not running.

Source/Core/DolphinWX/ConfigMain.cpp

@@ -882,6 +882,8 @@ void CConfigMain::CoreSettingsChanged(wxCommandEvent& event)
 	{
 	// Core - Basic
 	case ID_CPUTHREAD:
+		if (Core::GetState() != Core::CORE_UNINITIALIZED)
+			return;
 		SConfig::GetInstance().m_LocalCoreStartupParameter.bCPUThread = CPUThread->IsChecked();
 		break;
 	case ID_IDLESKIP:

Source/Core/DolphinWX/FrameTools.cpp

@@ -888,6 +888,8 @@ void CFrame::ToggleDisplayMode(bool bFullscreen)
 // Prepare the GUI to start the game.
 void CFrame::StartGame(const std::string& filename)
 {
+	if (m_bGameLoading)
+		return;
 	m_bGameLoading = true;
 
 	if (m_ToolBar)

Source/Core/DolphinWX/VideoConfigDiag.h

@@ -20,6 +20,7 @@
 #include "Common/CommonTypes.h"
 #include "Common/SysConf.h"
 #include "Core/ConfigManager.h"
+#include "Core/Core.h"
 #include "Core/CoreParameter.h"
 #include "DolphinWX/WxUtils.h"
 #include "VideoCommon/VideoBackendBase.h"
@@ -85,7 +86,7 @@ protected:
 		VideoBackend* new_backend = g_available_video_backends[ev.GetInt()];
 		if (g_video_backend != new_backend)
 		{
-			bool do_switch = true;
+			bool do_switch = Core::GetState() == Core::CORE_UNINITIALIZED;
 			if (new_backend->GetName() == "Software Renderer")
 			{
 				do_switch = (wxYES == wxMessageBox(_("Software rendering is an order of magnitude slower than using the other backends.\nIt's only useful for debugging purposes.\nDo you really want to enable software rendering? If unsure, select 'No'."),