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.
openerp/addons/base/ir/ir_qweb.py
g_att += ''.join(
                _build_attribute(name, value)
                for name, value in self.attributes(
                    cr, uid, field_name, record, options,
                    source_element, g_att, t_att, qweb_context,
                    context=context)
            )
        return self.render_element(cr, uid, source_element, t_att, g_att,
                                   qweb_context, content)
    def qweb_object(self):
        return self.pool['ir.qweb']
    def render_element(self, cr, uid, source_element, t_att, g_att,
                       qweb_context, content):
        """ render_element(cr, uid, source_element, t_att, g_att, qweb_context, content)
        Final rendering hook, by default just calls ir.qweb's ``render_element``
        """
        return self.qweb_object().render_element(
            source_element, t_att, g_att, qweb_context, content or '')
    def user_lang(self, cr, uid, context):
        """ user_lang(cr, uid, context)
        Fetches the res.lang object corresponding to the language code stored
        in the user's context. Fallbacks to en_US if no lang is present in the
        context *or the language code is not valid*.
        :returns: res.lang browse_record
        """
        if context is None: context = {}
        lang_code = context.get('lang') or 'en_US'
        Lang = self.pool['res.lang']
        return Lang.browse(cr, uid, Lang._lang_get(cr, uid, lang_code), context=context)
class IntegerConverter(osv.AbstractModel):