ANGLE keeps bound the previous bound shader for draw calls with no shader associated to some stages

When the state is marked as dirty with markAllStateDirty, ANGLE resets the 
applied shaders to NULL however it does not unbind them from the D3D11 pipeline.

Hence ANGLE is tricked into believing that no shader is bound to some stages 
when actually they are.

This is a problem with geometry shaders (3D texture transfer, point sprite) and 
transform feedback (with no PS associated).

For instance, dEQP functional.texture.specification.teximage3d_pbo.*_3d are 
failing because:
PixelTransfer11::copyBufferToTexture copies using a GS
PixelTransfer11::copyBufferToTexture calls markAllStateDirty
then the next draw call — which should only use a VS/PS — fails with:
ID3D11DeviceContext::DrawIndexed: Vertex Shader - Geometry Shader linkage 
error: Signatures between stages are incompatible. Semantic 'TEXCOORD' is 
defined for mismatched hardware registers between the output stage and input 
stage. [ EXECUTION ERROR #343: DEVICE_SHADER_LINKAGE_REGISTERINDEX]

Original issue reported on code.google.com by Gregory....@imgtec.com on 16 Jan 2015 at 4:57

thanpv-lifortevn / angleproject

ANGLE keeps bound the previous bound shader for draw calls with no shader associated to some stages #872