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.
"""
            Checks if the bundle contains any sass/less content, then compiles it to css.
            Returns the bundle's flat css.
        """
        for atype in (SassStylesheetAsset, LessStylesheetAsset):
            assets = [asset for asset in self.stylesheets if isinstance(asset, atype)]
            if assets:
                cmd = assets[0].get_command()
                source = '\n'.join([asset.get_source() for asset in assets])
                compiled = self.compile_css(cmd, source)
                fragments = self.rx_css_split.split(compiled)