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.
if "value" in template_attributes:
            qwebcontext[template_attributes["set"]] = self.eval_object(template_attributes["value"], qwebcontext)
        elif "valuef" in template_attributes:
            qwebcontext[template_attributes["set"]] = self.eval_format(template_attributes["valuef"], qwebcontext)
        else:
            qwebcontext[template_attributes["set"]] = self.render_element(element, template_attributes, generated_attributes, qwebcontext)
        return ""
    def render_tag_field(self, element, template_attributes, generated_attributes, qwebcontext):
        """ eg: <span t-record="browse_record(res.partner, 1)" t-field="phone">+1 555 555 8069</span>"""
        node_name = element.tag
        assert node_name not in ("table", "tbody", "thead", "tfoot", "tr", "td",
                                 "li", "ul", "ol", "dl", "dt", "dd"),\
            "RTE widgets do not work correctly on %r elements" % node_name
        assert node_name != 't',\
            "t-field can not be used on a t element, provide an actual HTML node"
        record, field_name = template_attributes["field"].rsplit('.', 1)
        record = self.eval_object(record, qwebcontext)
        field = record._fields[field_name]
        foptions = self.eval_format(template_attributes.get('field-options') or '{}', qwebcontext)
        options = json.loads(foptions)
        field_type = get_field_type(field, options)
        converter = self.get_converter_for(field_type)
        return converter.to_html(qwebcontext.cr, qwebcontext.uid, field_name, record, options,
                                 element, template_attributes, generated_attributes, qwebcontext, context=qwebcontext.context)
    def get_converter_for(self, field_type):