Named arguments after unnamed arguments not being passed in correctly

[davidkpiano]

TEST:

@function foo($a, $b: null, $c: false) {
  @return $c;
}

@function bar($args...) {
  @return call(foo, $args...);
}

test {
  test: bar(3, $c: true);
}

EXPECTED (Ruby Sass):

test {
  test: true;
}

ACTUAL (Libsass):

test {
  test: false;
}

[xzyfer]

Specs added sass/sass-spec#527

[xzyfer]

This was fixed by #1588