Fixes #32645 Trailing hyphen is removed in JHTML::_('select.options')

### Issue
A list option similar to `- select value -` is currently truncated to `- select value` when built using JHtmlSelect::options (like in JHtmlSelect::genericlist or the list formfield).

#### Tracker
http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_id=8103&tracker_item_id=32645