Impacted versions: ODOO 10

Problem.
If i print a invoice with a negative amount, the pdf shows a vertical bar instead of a minus symbol.
![image](https://cloud.githubusercontent.com/assets/28800797/26237253/b07fadb0-3c74-11e7-86c2-c8688d82b5a5.png)

I have tried to install a new pdf reader, but with no result.
t_render = None
        template_attributes = {}
        debugger = element.get('t-debug')
        if debugger is not None:
            if openerp.tools.config['dev_mode']:
                __import__(debugger).set_trace()  
            else:
                _logger.warning("@t-debug in template '%s' is only available in --dev mode" % qwebcontext['__template__'])
        for (attribute_name, attribute_value) in element.attrib.iteritems():
            attribute_name = unicode(attribute_name)
            if attribute_name == "groups":
                cr = qwebcontext.get('request') and qwebcontext['request'].cr or None