[CommonHMTL] mover with mpadded can be misaligned.

This example misaligns the arrows in CommonHTML

<math>
  <mover>
    <mpadded height=".2em">
      <mo minsize="2em">&#x2190;</mo>
    </mpadded>
    <mo minsize="2em">&#x2192;</mo>
  </mover>
</math>

It is correct in HTML-CSS and SVG modes.