so remove the case for it being NULL.

tell the RPC runtime that the call failed.

CoRevertToSelf on top of CoGetCallContext, which is a stub.

- Based on comments from H. Verbeet
- Changed the distinction from .rgba & .xyzw masks to only use .xyzw
  in GLSL shaders.  They are interchangeable, and only served to make
  the trace look more intuitive, but they don't always apply as-is, so
  we'll just leave everything to .xyzw.
- Got rid of the "UseProgramObjectARB(0)" call in drawprim.  If there
  is no shader set on the next primitive, then that primitive will
  call UseProgramObjectARB(0) when it begins to draw.

could end up using the previously allocated memory even if it isn't
the right size, causing heap corruption.

rpcrt4: Initialise pStubMsg->MemorySize to zero before calling ComplexStructMemorySize from NdrComplexArrayUnmarshall.