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.
content = self.rx_sourceMap.sub('', self.content)
        
        content = re.sub(r'/\*.*?\*/', '', content, flags=re.S)
        
        content = re.sub(r'\s+', ' ', content)
        content = re.sub(r' *([{}]) *', r'\1', content)
        return self.with_header(content)
    def to_html(self):
        media = (' media="%s"' % werkzeug.utils.escape(self.media)) if self.media else ''
        if self.url:
            href = self.html_url
            return '<link rel="stylesheet" href="%s" type="text/css"%s/>' % (href, media)
        else:
            return '<style type="text/css"%s>%s</style>' % (media, self.with_header())
class PreprocessedCSS(StylesheetAsset):
    rx_import = None
    def __init__(self, *args, **kw):
        super(PreprocessedCSS, self).__init__(*args, **kw)
        self.html_url_format = '%%s/%s/%%s.css' % self.bundle.xmlid
        self.html_url_args = tuple(self.url.rsplit('/', 1))
    def get_source(self):
        content = self.inline or self._fetch_content()
        return "/*! %s */\n%s" % (self.id, content)
    def get_command(self):
        raise NotImplementedError
class SassStylesheetAsset(PreprocessedCSS):