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.
self.media = kw.pop('media', None)
        super(StylesheetAsset, self).__init__(*args, **kw)
    @property
    def content(self):
        content = super(StylesheetAsset, self).content
        if self.media:
            content = '@media %s { %s }' % (self.media, content)
        return content
    def _fetch_content(self):
        try:
            content = super(StylesheetAsset, self)._fetch_content()
            web_dir = os.path.dirname(self.url)
            if self.rx_import:
                content = self.rx_import.sub(
                    r"""@import \1%s/""" % (web_dir,),
                    content,
                )
            if self.rx_url:
                content = self.rx_url.sub(
                    r"url(\1%s/" % (web_dir,),
                    content,
                )
            if self.rx_charset:
                
                content = self.rx_charset.sub('', content)
            return content
        except AssetError, e:
            self.bundle.css_errors.append(e.message)
            return ''
    def minify(self):