Prevent an infinite loop when the trimmed text is shorter than the condensed length.

When the contents of the element are only text (html.length == text.length) and the substring is as long as or longer than the condensed length (loc >= opts.condensedLength) and the trimmed body is shorter than the condensed length (clone.text().length < opts.condensedLength), then delta will be zero and the do/while loop will be stuck in an infinite loop.
Merge pull request #6 from eventualbuddha/patch-1

Prevent an infinite loop when the trimmed text is shorter than the condensed length