glVertexAttribPointer validation

glVertexAttribPointer validation

GL_INVALID_OPERATION is generated if a non-zero vertex array object
is bound, zero is bound to the GL_ARRAY_BUFFER buffer object binding
point and the pointer argument is not NULL.

Change-Id: I48e73dca96bac2bd0496c202785e46e7d754dc11
Reviewed-on: https://swiftshader-review.googlesource.com/13830
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>