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.
fragments = html.fragments_fromstring(self.html)
        for el in fragments:
            if isinstance(el, basestring):
                self.remains.append(el)
            elif isinstance(el, html.HtmlElement):
                src = el.get('src', '')
                href = el.get('href', '')
                atype = el.get('type')
                media = el.get('media')
                if el.tag == 'style':
                    if atype == 'text/sass' or src.endswith('.sass'):
                        self.stylesheets.append(SassStylesheetAsset(self, inline=el.text, media=media))
                    elif atype == 'text/less' or src.endswith('.less'):
                        self.stylesheets.append(LessStylesheetAsset(self, inline=el.text, media=media))
                    else:
                        self.stylesheets.append(StylesheetAsset(self, inline=el.text, media=media))
                elif el.tag == 'link' and el.get('rel') == 'stylesheet' and self.can_aggregate(href):
                    if href.endswith('.sass') or atype == 'text/sass':
                        self.stylesheets.append(SassStylesheetAsset(self, url=href, media=media))
                    elif href.endswith('.less') or atype == 'text/less':
                        self.stylesheets.append(LessStylesheetAsset(self, url=href, media=media))