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
rx_indent = re.compile(r'^( +|\t+)', re.M)
    indent = None
    reindent = '    '
    def get_source(self):
        content = textwrap.dedent(self.inline or self._fetch_content())
        def fix_indent(m):
            
            ind = m.group()
            if self.indent is None:
                self.indent = ind
                if self.indent == self.reindent:
                    
                    raise StopIteration()
            return ind.replace(self.indent, self.reindent)
        try:
            content = self.rx_indent.sub(fix_indent, content)
        except StopIteration:
            pass
        return "/*! %s */\n%s" % (self.id, content)
    def get_command(self):
        try:
            sass = find_in_path('sass')
        except IOError:
            sass = 'sass'
        return [sass, '--stdin', '-t', 'compressed', '--unix-newlines', '--compass',
                '-r', 'bootstrap-sass']
class LessStylesheetAsset(PreprocessedCSS):