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
""" Used to convert a t-field specification into an output HTML field.
    :meth:`~.to_html` is the entry point of this conversion from QWeb, it:
    * converts the record value to html using :meth:`~.record_to_html`
    * generates the metadata attributes (``data-oe-``) to set on the root
      result node
    * generates the root result node itself through :meth:`~.render_element`
    """
    _name = 'ir.qweb.field'
    def attributes(self, cr, uid, field_name, record, options,
                   source_element, g_att, t_att, qweb_context,
                   context=None):
        """ attributes(cr, uid, field_name, record, options, source_element, g_att, t_att, qweb_context, context=None)
        Generates the metadata attributes (prefixed by ``data-oe-`` for the
        root node of the field conversion. Attribute values are escaped by the
        parent.
        The default attributes are:
        * ``model``, the name of the record's model
        * ``id`` the id of the record to which the field belongs
        * ``field`` the name of the converted field
        * ``type`` the logical field type (widget, may not match the field's
          ``type``, may not be any Field subclass name)
        * ``translate``, a boolean flag (``0`` or ``1``) denoting whether the
          field is translatable