Fix UnicodeDecodeError with non-ascii content when using inline compression

This fixes a UnicodeDecodeError that happens if you are using the templatetag with the inline option and non-ascii content.

It appeared in #271, which was supposed to fix #270, which was a similar bug but with jinja2. The fix seems wrong to me: first, it only applies to one case - it doesn't affect cached result - and second the result is already an unicode string at this point (well, django.utils.safestring.SafeUnicode), so no decoding is necessary.

This fixes #305, I've included @marselester 's original failing test in the pull request, and that fixes it. In addition, it still passes the test originally added for #271.