svg_mask_element: avoid dangling style.
svg_mask_element: avoid dangling style.

janmarthedal/mathml2svg,gjtorikian/lasem,wavewave/lasem,janmarthedal/mathml2svg,janmarthedal/mathml2svg,gjtorikian/lasem,gjtorikian/lasem,wavewave/lasem,wavewave/lasem,gjtorikian/lasem,janmarthedal/mathml2svg,wavewave/lasem