SDL: Apply shutdown race condition fix.

Qt/QtMain.cpp

@@ -208,6 +208,7 @@ void MainUI::EmuThreadFunc() {
 	emuThreadState = (int)EmuThreadState::STOPPED;
 
 	NativeShutdownGraphics();
+	graphicsContext->StopThread();
 }
 
 void MainUI::EmuThreadStart() {

Qt/QtMain.h

@@ -82,6 +82,11 @@ public:
 		renderManager_->ThreadEnd();
 	}
 
+	void StopThread() override {
+		renderManager_->WaitUntilQueueIdle();
+		renderManager_->StopThread();
+	}
+
 private:
 	Draw::DrawContext *draw_ = nullptr;
 	GLRenderManager *renderManager_ = nullptr;

SDL/SDLGLGraphicsContext.h

@@ -38,6 +38,11 @@ public:
 		renderManager_->ThreadEnd();
 	}
 
+	void StopThread() override {
+		renderManager_->WaitUntilQueueIdle();
+		renderManager_->StopThread();
+	}
+
 private:
 	Draw::DrawContext *draw_ = nullptr;
 	SDL_Window *window_;

SDL/SDLMain.cpp

@@ -423,6 +423,7 @@ static void EmuThreadFunc(GraphicsContext *graphicsContext) {
 	emuThreadState = (int)EmuThreadState::STOPPED;
 
 	NativeShutdownGraphics();
+	graphicsContext->StopThread();
 }
 
 static void EmuThreadStart(GraphicsContext *context) {