st/mesa: don't update unrelated states in non-draw calls such as Clear

st/mesa: don't update unrelated states in non-draw calls such as Clear

If a VAO isn't bound and u_vbuf isn't enabled because of the Core profile,
we'll get user vertex buffers in drivers if we update vertex buffers
in glClear. So don't do that.

This fixes a regression since disabling u_vbuf for Core profiles.

Reviewed-by: Brian Paul <brianp@vmware.com>