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.
try:
            return qwebcontext.safe_eval(expr)
        except Exception:
            template = qwebcontext.get('__template__')
            raise_qweb_exception(message="Could not evaluate expression %r" % expr, expression=expr, template=template)
    def eval_object(self, expr, qwebcontext):
        return self.eval(expr, qwebcontext)
    def eval_str(self, expr, qwebcontext):
        if expr == "0":
            return qwebcontext.get(0, '')
        val = self.eval(expr, qwebcontext)
        if isinstance(val, unicode):
            return val.encode("utf8")
        if val is False or val is None:
            return ''
        return str(val)
    def eval_format(self, expr, qwebcontext):
        expr, replacements = self._format_regex.subn(
            lambda m: self.eval_str(m.group(1) or m.group(2), qwebcontext),
            expr
        )
        if replacements:
            return expr
        try:
            return str(expr % qwebcontext)
        except Exception:
            template = qwebcontext.get('__template__')
            raise_qweb_exception(message="Format error for expression %r" % expr, expression=expr, template=template)
    def eval_bool(self, expr, qwebcontext):