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
source_element, t_att, g_att, qweb_context, context=None):
        """ to_html(cr, uid, field_name, record, options, source_element, t_att, g_att, qweb_context, context=None)
        Converts a ``t-field`` to its HTML output. A ``t-field`` may be
        extended by a ``t-field-options``, which is a JSON-serialized mapping
        of configuration values.
        A default configuration key is ``widget`` which can override the
        field's own ``_type``.
        """
        try:
            content = self.record_to_html(cr, uid, field_name, record, options, context=context)
            if options.get('html-escape', True):
                content = escape(content)
            elif hasattr(content, '__html__'):
                content = content.__html__()
        except Exception:
            _logger.warning("Could not get field %s for model %s",
                            field_name, record._name, exc_info=True)
            content = None
        inherit_branding = context and context.get('inherit_branding')
        if not inherit_branding and context and context.get('inherit_branding_auto'):
            inherit_branding = self.pool['ir.model.access'].check(cr, uid, record._name, 'write', False, context=context)
        translate = context and context.get('edit_translations') and context.get('translatable') and getattr(record._fields[field_name], 'translate', False)
        if inherit_branding or translate: