D3D11: Attempt fix for WinRT issue #632.

src/renderer_d3d11.cpp

@@ -2224,6 +2224,9 @@ BX_PRAGMA_DIAGNOSTIC_POP();
 				}
 				else
 				{
+					m_deviceCtx->ClearState();
+					m_deviceCtx->Flush();
+
 					if (resize)
 					{
 						m_deviceCtx->OMSetRenderTargets(1, s_zero.m_rtv, NULL);