Fixed truncate filter from text extension

When truncating, we want the text to be shorter than the given limit.
Previously, when asking to preserve words, the truncate filter would return text larger.

Example:

* input:` 'No one expects the spanish inquisition'|truncate(21, true, '…')`
* output: `'No one expects the spanish…'`
* expected: `'No one expects the…'`