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.
return self.checksum[0:7]
    @lazy_property
    def checksum(self):
        """
        Not really a full checksum.
        We compute a SHA1 on the rendered bundle + max linked files last_modified date
        """
        check = self.html + str(self.last_modified)
        return hashlib.sha1(check).hexdigest()
    def clean_attachments(self, type):
        """ Takes care of deleting any outdated ir.attachment records associated to a bundle before
        saving a fresh one.
        When `type` is css we need to check that we are deleting a different version (and not *any*
        version) because css may be paginated and, therefore, may produce multiple attachments for
        the same bundle's version.
        When `type` is js we need to check that we are deleting a different version (and not *any*
        version) because, as one of the creates in `save_attachment` can trigger a rollback, the
        call to `clean_attachments ` is made at the end of the method in order to avoid the rollback
        of an ir.attachment unlink (because we cannot rollback a removal on the filestore), thus we
        must exclude the current bundle.
        """
        ira = self.registry['ir.attachment']
        domain = [
            ('url', '=like', '/web/content/%-%/{0}%.{1}'.format(self.xmlid, type)),  
            '!', ('url', '=like', '/web/content/%-{}/%'.format(self.version))
        ]
        attachment_ids = ira.search(self.cr, openerp.SUPERUSER_ID, domain, context=self.context)
        return ira.unlink(self.cr, openerp.SUPERUSER_ID, attachment_ids, context=self.context)
    def get_attachments(self, type, inc=None):