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
_name = 'ir.qweb.field.datetime'
    _inherit = 'ir.qweb.field'
    def value_to_html(self, cr, uid, value, field, options=None, context=None):
        if not value: return ''
        lang = self.user_lang(cr, uid, context=context)
        locale = babel.Locale.parse(lang.code)
        if isinstance(value, basestring):
            value = datetime.datetime.strptime(
                value, openerp.tools.DEFAULT_SERVER_DATETIME_FORMAT)
        value = fields.datetime.context_timestamp(
            cr, uid, timestamp=value, context=context)
        if options and 'format' in options:
            pattern = options['format']
        else:
            strftime_pattern = (u"%s %s" % (lang.date_format, lang.time_format))
            pattern = openerp.tools.posix_to_ldml(strftime_pattern, locale=locale)
        if options and options.get('hide_seconds'):
            pattern = pattern.replace(":ss", "").replace(":s", "")
        return babel.dates.format_datetime(value, format=pattern, locale=locale)
    def record_to_html(self, cr, uid, field_name, record, options, context=None):
        field = field = record._fields[field_name]
        value = record[field_name]
        return self.value_to_html(
            cr, uid, value, field, options=options, context=dict(context, **record.env.context))
class TextConverter(osv.AbstractModel):