Fix FilterAndSortCandidates behavior

While working on #307 i've noticed another bug. When ``g:ycm_min_num_of_chars_for_completion`` is set to 0 ultisnips_completer returns a list instead of dict, so the ``<snip>`` type and description is abscent. Check the screenshot:

![wrong](https://f.cloud.github.com/assets/1290755/484046/7f7c89b8-b8cf-11e2-82b7-26147004ae48.jpg)

This problem was introduced in c3b7e5576258d956a8b059b0ee86f147d67e6fb5. Currently  ``FilterAndSortCandidates(data, 'word', '')`` when ``data`` type is dict returns a list ( generated from ``'word'`` dict key ) while  ``FilterAndSortCandidates(data, '', '')`` is working as intended ( returns ``data`` ).