D3D9: Check for a NULL shader in IDirect3DDevice9Impl_GetVertexShader before getting the parent.

[H. Verbeet]

Currently wine dies when calling IDirect3DDevice9Impl_GetVertexShader
while a NULL shader is set. This patch fixes that.

Changelog:
  - Check for a NULL shader in IDirect3DDevice9Impl_GetVertexShader
before getting the parent.
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4c44e6331ed128c516e9a8d467abd5c55f682f5c
diff --git a/dlls/d3d9/vertexshader.c b/dlls/d3d9/vertexshader.c
index e4f76b9..034b097 100644
--- a/dlls/d3d9/vertexshader.c
+++ b/dlls/d3d9/vertexshader.c
@@ -148,7 +148,7 @@ HRESULT WINAPI IDirect3DDevice9Impl_GetV
 
     TRACE("(%p) : Relay  device@%p\n", This, This->WineD3DDevice);
     hrc = IWineD3DDevice_GetVertexShader(This->WineD3DDevice, &pShader);
-    if(hrc == D3D_OK){
+    if(hrc == D3D_OK && pShader != NULL){
        hrc = IWineD3DVertexShader_GetParent(pShader, (IUnknown **)ppShader);
        IWineD3DVertexShader_Release(pShader);
     } else {