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.
_name = 'ir.qweb.field.qweb'
    _inherit = 'ir.qweb.field.many2one'
    def record_to_html(self, cr, uid, field_name, record, options=None, context=None):
        if not getattr(record, field_name):
            return None
        view = getattr(record, field_name)
        if view._model._name != "ir.ui.view":
            _logger.warning("%s.%s must be a 'ir.ui.view' model." % (record, field_name))
            return None
        ctx = (context or {}).copy()
        ctx['object'] = record
        html = view.render(ctx, engine='ir.qweb', context=ctx).decode('utf8')
        return HTMLSafe(html)
class QwebWidget(osv.AbstractModel):
    _name = 'ir.qweb.widget'
    def _format(self, inner, options, qwebcontext):
        return self.pool['ir.qweb'].eval_str(inner, qwebcontext)
    def format(self, inner, options, qwebcontext):
        return escape(self._format(inner, options, qwebcontext))
class QwebWidgetMonetary(osv.AbstractModel):