st/nine: Implement dummy vbo behaviour when vs is missing inputs

st/nine: Implement dummy vbo behaviour when vs is missing inputs

Use a dummy vertex buffer object when vs inputs have no corresponding
entries in the vertex declaration. This dummy buffer will give to the
shader float4(0,0,0,0).

This fixes several artifacts on some games.

Signed-off-by: Axel Davy <axel.davy@ens.fr>
Signed-off-by: Tiziano Bacocco <tizbac2@gmail.com>