Make OpenGL render thread shutdown more robust.

Windows/GPU/WindowsGLContext.cpp

@@ -485,10 +485,15 @@ void WindowsGLContext::ThreadStart() {
 	renderManager_->ThreadStart(draw_);
 }
 
-bool WindowsGLContext::ThreadFrame(bool waitIfEmpty) {
-	return renderManager_->ThreadFrame(waitIfEmpty);
+bool WindowsGLContext::ThreadFrame() {
+	return renderManager_->ThreadFrame();
 }
 
 void WindowsGLContext::ThreadEnd() {
 	renderManager_->ThreadEnd();
 }
+
+void WindowsGLContext::NotifyEmuThreadExit() {
+	// renderManager_->SetSkipGLCalls();   // not necessary on desktop, maybe unadvisable?
+	renderManager_->NotifyEmuThreadExit();
+}

Windows/GPU/WindowsGLContext.h

@@ -33,7 +33,11 @@ public:
 	// If these are used, they are called from the render thread. If NeedsRenderThread is false, they are not called.
 	void ThreadStart() override;
 	void ThreadEnd() override;
-	bool ThreadFrame(bool waitIfEmpty) override;
+
+	// If this returns false, the render thread has been instructed to exit.
+	bool ThreadFrame() override;
+
+	void NotifyEmuThreadExit() override;
 
 	Draw::DrawContext *GetDrawContext() override { return draw_; }