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.
openerp/addons/base/ir/ir_qweb.py
else:
                        self.stylesheets.append(StylesheetAsset(self, url=href, media=media))
                elif el.tag == 'script' and not src:
                    self.javascripts.append(JavascriptAsset(self, inline=el.text))
                elif el.tag == 'script' and self.can_aggregate(src):
                    self.javascripts.append(JavascriptAsset(self, url=src))
                else:
                    self.remains.append(html.tostring(el))
            else:
                try:
                    self.remains.append(html.tostring(el))
                except Exception:
                    
                    raise NotImplementedError
    def can_aggregate(self, url):
        return not urlparse(url).netloc and not url.startswith('/web/content')
    def to_html(self, sep=None, css=True, js=True, debug=False, async=False, qwebcontext=None):
        if sep is None:
            sep = '\n            '
        response = []
        if debug:
            if css and self.stylesheets:
                if not self.is_css_preprocessed():
                    self.preprocess_css(debug=debug)
                    if self.css_errors:
                        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: