DocBook: in a table, fix a typo in a condition.

DocBook: in a table, fix a typo in a condition.

Before this patch, all table cells had a semicolon at the beginning of their style:

<td style='; border-bottom:

This unwanted behaviour is only due to a typo in a condition when concatenating two styles: the previous code was checking the second part of the style once the first was output, instead of the first one.