[d3d11] Fixed FinishCommandList

- ppCommandList is optional.
- We need to call RestoreState in order to set up the current context
  state for the new command list.

src/d3d11/d3d11_context_def.cpp

@@ -43,11 +43,14 @@ namespace dxvk {
   HRESULT STDMETHODCALLTYPE D3D11DeferredContext::FinishCommandList(
           WINBOOL             RestoreDeferredContextState,
           ID3D11CommandList   **ppCommandList) {
-    *ppCommandList = m_commandList.ref();
+    if (ppCommandList != nullptr)
+      *ppCommandList = m_commandList.ref();
     m_commandList = CreateCommandList();
     
     if (!RestoreDeferredContextState)
       ClearState();
+    else
+      RestoreState();
     
     return S_OK;
   }