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.
openerp/addons/base/ir/ir_qweb.py
self._render_tag[tag] = func
    def get_template(self, name, qwebcontext):
        origin_template = qwebcontext.get('__caller__') or qwebcontext['__stack__'][0]
        try:
            document = qwebcontext.loader(name)
        except ValueError:
            raise_qweb_exception(QWebTemplateNotFound, message="Loader could not find template %r" % name, template=origin_template)
        if hasattr(document, 'documentElement'):
            dom = document
        elif document.startswith("<?xml"):
            dom = etree.fromstring(document)
        else:
            dom = etree.parse(document).getroot()
        res_id = isinstance(name, (int, long)) and name or None
        for node in dom:
            if node.get('t-name') or (res_id and node.tag == "t"):
                return node
        raise QWebTemplateNotFound("Template %r not found" % name, template=origin_template)
    def eval(self, expr, qwebcontext):