Should error when interpolating nothing

[xzyfer]

These examples should produce the error show but do not

$foo: #{};

Should produce this error

Error: Invalid CSS after "$foo: #{": expected expression (e.g. 1px, bold), was "};"
        on line 1 of test.scss
  Use --trace for backtrace.

---

foo {
  bar: #{};
}

Should produce this error

Error: Invalid CSS after "  bar: #{": expected expression (e.g. 1px, bold), was "};"
        on line 2 of test.scss
  Use --trace for backtrace.

Specs added sass/sass-spec#324

[saper]

assignment and property tests from sass/sass-spec#324 do not fail on libsass 3.3.0-beta2 (as they probably should).

[xzyfer]

Confirm this has regressed in 3.3

[xzyfer]

I have a fix for this. Will publish when I'm home.