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.
for jscript in self.javascripts:
                    response.append(jscript.to_html())
        else:
            if qwebcontext is None:
                qwebcontext = QWebContext(self.cr, self.uid, {})
            if css and self.stylesheets:
                css_attachments = self.css()
                if not self.css_errors:
                    for attachment in css_attachments:
                        el = etree.fromstring('<link href="%s" rel="stylesheet"/>' % attachment.url)
                        response.append(self.registry['ir.qweb'].render_node(el, qwebcontext))
                else:
                    msg = '\n'.join(self.css_errors)
                    self.stylesheets.append(StylesheetAsset(self, inline=self.css_message(msg)))
                    for style in self.stylesheets:
                        response.append(style.to_html())
            if js and self.javascripts:
                el = etree.fromstring('<script %s type="text/javascript" src="%s"></script>' % (async and 'async="async"' or '', self.js().url))
                response.append(self.registry['ir.qweb'].render_node(el, qwebcontext))
        response.extend(self.remains)
        return sep + sep.join(response)
    @lazy_property
    def last_modified(self):
        """Returns last modified date of linked files"""
        return max(itertools.chain(
            (asset.last_modified for asset in self.javascripts),
            (asset.last_modified for asset in self.stylesheets),
        ))
    @lazy_property
    def version(self):