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.
if self._content is None:
            self._content = self.inline or self._fetch_content()
        return self._content
    def _fetch_content(self):
        """ Fetch content from file or database"""
        try:
            self.stat()
            if self._filename:
                with open(self._filename, 'rb') as fp:
                    return fp.read().decode('utf-8')
            else:
                return self._ir_attach['datas'].decode('base64')
        except UnicodeDecodeError:
            raise AssetError('%s is not utf-8 encoded.' % self.name)
        except IOError:
            raise AssetNotFound('File %s does not exist.' % self.name)
        except:
            raise AssetError('Could not get content for %s.' % self.name)
    def minify(self):
        return self.content
    def with_header(self, content=None):
        if content is None:
            content = self.content
        return '\n/* %s */\n%s' % (self.name, content)
class JavascriptAsset(WebAsset):