Impacted versions: Odoo 11 on windows server 2012

Steps to reproduce: 
Create a new out invoice, select a product and set a negative amount for unit price.
Print the invoice.

Current behavior:
in PDF the char "-" is shown as "|" even if the total amount is correct (amount1 - amount2 = total)

Expected behavior:
the printed invoice should show the char "-"

Video/Screenshot link (optional):
![image](https://user-images.githubusercontent.com/37513316/42877323-8c712b2e-8a89-11e8-9690-27f00e08b6b2.png)

this is the negative item on odoo:
![image](https://user-images.githubusercontent.com/37513316/42877389-bf04eba2-8a89-11e8-91c0-e38059673b42.png)


def test_selection(self):
        [record] = self.Model.browse(self.cr, self.uid, [self.Model.create(self.cr, self.uid, {
            'selection': 2,
            'selection_str': 'C',
        })])
        converter = self.registry('ir.qweb.field.selection')
        field_name = 'selection'
        value = converter.record_to_html(self.cr, self.uid, field_name, record)
        self.assertEqual(value, "réponse B")
        field_name = 'selection_str'
        value = converter.record_to_html(self.cr, self.uid, field_name, record)
        self.assertEqual(value, "Qu'est-ce qu'il fout ce maudit pancake, tabernacle ?")
class TestHTMLExport(TestBasicExport):
    def test_html(self):
        converter = self.get_converter('html')
        input = '<span>span</span>'
        value = converter(input)
        self.assertEqual(value, input)
class TestDatetimeExport(TestBasicExport):
    def setUp(self):
        super(TestDatetimeExport, self).setUp()
        # 
        Users = self.registry('res.users')
        Users.write(self.cr, self.uid, self.uid, {
            'tz': 'Pacific/Niue'
        }, context=None)
    def test_date(self):