Merge pull request #1521 from am11/master

srv-scss: Changes for downstream v0.9.4
Nightly v2.3.4
Browser Link: Fixed NullReferenceException
srv-rtlcss: Prevent from throwing.
The problem is, when both rtlcss and autoprefixer
are enabled, it works fine with SCSS, but throws
with LESS.

When the code is too complicated,
the `result` object seems to have problem with
returning `result.css` member. When the code is
comparatively straight-forward, it throws a
slightly lenient error.

/cc @MohammadYounes