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
return self.copy()
class QWeb(orm.AbstractModel):
    """ Base QWeb rendering engine
    * to customize ``t-field`` rendering, subclass ``ir.qweb.field`` and
      create new models called :samp:`ir.qweb.field.{widget}`
    * alternatively, override :meth:`~.get_converter_for` and return an
      arbitrary model to use as field converter
    Beware that if you need extensions or alterations which could be
    incompatible with other subsystems, you should create a local object
    inheriting from ``ir.qweb`` and customize that.
    """
    _name = 'ir.qweb'
    _void_elements = frozenset([
        u'area', u'base', u'br', u'col', u'embed', u'hr', u'img', u'input',
        u'keygen', u'link', u'menuitem', u'meta', u'param', u'source',
        u'track', u'wbr'])
    _format_regex = re.compile(
        '(?:'
            
            '#\{(.+?)\}'
        ')|(?:'
            
            '\{\{(.+?)\}\}'
        ')')
    def __init__(self, pool, cr):