Also allow points drawing without gl_PointSize if transform feedback is
active.

Change-Id: I172d423e847b35b94ebaea102dd97b695575c828
Reviewed-on: https://chromium-review.googlesource.com/246100Tested-by: Gregoire Payen de La Garanderie <Gregory.Payen@imgtec.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>