When dealing with multiple Transform Feedback buffers, each of them needs to have their own offset, so when resuming from one to another we know exactly were to continue adding primitives. Fixes "spec@arb_transform_feedback2@change objects while paused (gles3)" piglit test. Signed-off-by: Juan A. Suarez Romero <jasuarez@igalia.com> Reviewed-by: Eric Engestrom <eric@igalia.com> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17373>