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.
""" This special 't-call' tag can be used in order to aggregate/minify javascript and css assets"""
        if len(element):
            
            
            
            template = qwebcontext.get('__template__')
            raise QWebException("t-call-assets cannot contain children nodes", template=template)
        xmlid = template_attributes['call-assets']
        cr, uid, context = [getattr(qwebcontext, attr) for attr in ('cr', 'uid', 'context')]
        bundle = AssetsBundle(xmlid, cr=cr, uid=uid, context=context, registry=self.pool)
        css = self.get_attr_bool(template_attributes.get('css'), default=True)
        js = self.get_attr_bool(template_attributes.get('js'), default=True)
        async = self.get_attr_bool(template_attributes.get('async'), default=False)
        return bundle.to_html(css=css, js=js, debug=bool(qwebcontext.get('debug')), async=async, qwebcontext=qwebcontext)
    def render_tag_set(self, element, template_attributes, generated_attributes, qwebcontext):