[REVIEW-3-5] fix for fdo#46220, infinite loop when exporting hidden column to html

[Markus Mohrhard]

Hey,

[1] fixes the infinite loop in html export when we try to skip a
hidden column. We need to increase nCol in this case to prevent that
we will always test the same column.

This fix is safe and simple and I think we should include it into 3-5.

Regards,
Markus

[1] http://cgit.freedesktop.org/libreoffice/core/commit/?id=c4744121f12fde51de2d92d2442d590d93725ffc