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.
name = unicode(element.tag)
        if inner:
            g_inner = inner.encode('utf-8') if isinstance(inner, unicode) else inner
        else:
            g_inner = [] if element.text is None else [self.render_text(element.text, element, qwebcontext)]
            for current_node in element.iterchildren(tag=etree.Element):
                try:
                    g_inner.append(self.render_node(current_node, qwebcontext,
                        generated_attributes= name == "t" and generated_attributes or ''))
                except QWebException:
                    raise
                except Exception:
                    template = qwebcontext.get('__template__')
                    raise_qweb_exception(message="Could not render element %r" % element.tag, node=element, template=template)
        inner = "".join(g_inner)
        trim = template_attributes.get("trim", 0)
        if trim == 0:
            pass
        elif trim == 'left':
            inner = inner.lstrip()
        elif trim == 'right':
            inner = inner.rstrip()