In DX8 the D3DSURFACE_DESC structure has a size field which needs to be set.

Implement check for NULL context handles if requested.

Call it with fMustAlloc set to TRUE instead to achieve the same result
without side-effects.

Use it in RPCRT4_SendAuth instead of writing out the data byte-by-byte.

    
This avoids having to export too many different message translation
functions.

Add simple struct tests.