It's not necessary to set the intersection rectangle in case the
intersection is empty.

BUG=chromium:830046
TEST=angle_end2end_tests

Change-Id: I0b99cdb7d6623b2d8a95dbe946a6eead6a44351d
Reviewed-on: https://chromium-review.googlesource.com/1021695Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>