Paints the right margin after editor paint event.

def _paint_margins(self, event):
        """ Paints the right margin after editor paint event. """
        font = QtGui.QFont(self.editor.font_name, self.editor.font_size +
                           self.editor.zoom_level)
        metrics = QtGui.QFontMetricsF(font)
        painter = QtGui.QPainter(self.editor.viewport())
        for pos, pen in zip(self._positions, self._pens):
            if pos < 0:
                # margin not visible
                continue
            offset = self.editor.contentOffset().x() + \
                self.editor.document().documentMargin()
            x_pos = round(metrics.width(' ') * pos) + offset
            painter.setPen(pen)
            painter.drawLine(x_pos, 0, x_pos, 2 ** 16)