Fix for rendering issues when calling GetDepthStencilSurface

[Alexander Dorofeyev]

Any reason this isn't tested? I don't know about this function in 
particular, but there have been games that were confused by NOT clearing 
output to NULL on error (not in GetDepthStencilSurface though).

Also regardless of setting or not-setting to NULL, the warning may have 
its uses when reading +d3d log in the process of debugging something.

Andrew Fenn wrote:
> When IWineD3DDevice_GetDepthStencilSurface returns WINED3DERR_NOTFOUND
> it was setting ppZStencilSurface to null. This was the cause of
> rendering issues with the 3d models in spore.
>