Fix exit crash on Windows ARM64 with D3D11 (and probably also x64 Windows, but couldn't repro that)

Windows/EmuThread.cpp

@@ -335,6 +335,7 @@ void MainThreadFunc() {
 	g_graphicsContext->Shutdown();
 
 	delete g_graphicsContext;
+	g_graphicsContext = nullptr;
 
 	RECT rc;
 	if (console && GetWindowRect(console, &rc) && !IsIconic(console)) {

Windows/GPU/D3D11Context.cpp

@@ -256,6 +256,19 @@ void D3D11Context::Shutdown() {
 	}
 #endif
 
+#ifdef _DEBUG
+	d3dDebug_ = nullptr;
+	d3dInfoQueue_ = nullptr;
+#endif
+
+	// Important that we release before we unload the DLL, otherwise we may crash on shutdown.
+	bbRenderTargetTex_ = nullptr;
+	bbRenderTargetView_ = nullptr;
+	context1_ = nullptr;
+	context_ = nullptr;
+	device1_ = nullptr;
+	device_ = nullptr;
 	hWnd_ = nullptr;
+
 	UnloadD3D11();
 }