Loop condition node may be a declaration node when coming from the
parser, so it shouldn't be casted to TIntermTyped*.

BUG=chromium:738281
TEST=angle_unittests under CFI

Change-Id: Ie98befc4b02b1261949049ddff49404d73db8478
Reviewed-on: https://chromium-review.googlesource.com/558083Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>