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.
at_rules = fragments.pop(0)
                if at_rules:
                    
                    self.stylesheets.insert(0, StylesheetAsset(self, inline=at_rules))
                while fragments:
                    asset_id = fragments.pop(0)
                    asset = next(asset for asset in self.stylesheets if asset.id == asset_id)
                    asset._content = fragments.pop(0)
                    if debug:
                        try:
                            ira = self.registry['ir.attachment']
                            fname = os.path.basename(asset.url)
                            url = asset.html_url
                            with self.cr.savepoint():
                                ira.create(self.cr, openerp.SUPERUSER_ID, dict(
                                    datas=asset.content.encode('utf8').encode('base64'),
                                    mimetype='text/css',
                                    type='binary',
                                    name=url,
                                    url=url,
                                    datas_fname=fname,
                                    res_model=False,
                                    res_id=False,
                                ), context=self.context)
                            if self.context.get('commit_assetsbundle') is True:
                                self.cr.commit()
                        except psycopg2.Error:
                            pass
        return '\n'.join(asset.minify() for asset in self.stylesheets)
    def compile_css(self, cmd, source):