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.
currency = self.create(self.Currency, name="Test", symbol=u"test")
        obj = self.create(self.Model, value=-0.12)
        converted = self.convert(obj, dest=currency)
        self.assertEqual(
            converted,
            '<span data-oe-model="{obj._model._name}" data-oe-id="{obj.id}" '
                  'data-oe-field="value" data-oe-type="monetary" '
                  'data-oe-expression="obj.value">'
                      u'<span class="oe_currency_value">\u20110.12</span>'
                      u'\N{NO-BREAK SPACE}{symbol}</span>'.format(
                obj=obj,
                symbol=currency.symbol.encode('utf-8')
            ).encode('utf-8'),)
    def test_currency_pre(self):
        currency = self.create(
            self.Currency, name="Test", symbol=u"test", position='before')
        obj = self.create(self.Model, value=0.12)
        converted = self.convert(obj, dest=currency)
        self.assertEqual(
            converted,
            '<span data-oe-model="{obj._model._name}" data-oe-id="{obj.id}" '
                  'data-oe-field="value" data-oe-type="monetary" '
                  'data-oe-expression="obj.value">'
                      u'{symbol}\N{NO-BREAK SPACE}'
                      '<span class="oe_currency_value">0.12</span>'
                      '</span>'.format(
                obj=obj,
                symbol=currency.symbol.encode('utf-8')
            ).encode('utf-8'),)
    def test_currency_precision(self):