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.
import json
import os
import datetime
from lxml import etree
from openerp.tests import common
from openerp.tools import html_escape as e
from openerp.addons.base.ir import ir_qweb
directory = os.path.dirname(__file__)
class TestExport(common.TransactionCase):
    _model = None
    def setUp(self):
        super(TestExport, self).setUp()
        self.Model = self.registry(self._model)
    def get_field(self, name):
        return self.Model._fields[name]
    def get_converter(self, name, type=None):
        field = self.get_field(name)
        for postfix in type, field.type, '':
            fs = ['ir', 'qweb', 'field']
            if postfix is None: continue
            if postfix: fs.append(postfix)
            try:
                model = self.registry('.'.join(fs))
                break
            except KeyError: pass
        return lambda value, options=None, context=None: e(model.value_to_html(
            self.cr, self.uid, value, field, options=options, context=context))
class TestBasicExport(TestExport):