Fixup
b29b3eb1: fix broken xml syntax
This commit addresses two issues:
1/ the embarassing one: the member SetMode::old_text_level_ was
declared as bool instead of int. This means that is was definitely
not a proper backup variable!
2/ a robustness issue: replace two consecutive test for isTest() by a
boolean veriable that is used twice. This makes sure that <mrow>
cannot be output without the corresponding </mrow>.
Part of bug #13069.
(cherry picked from commit
a268fe096a58a7818554a7da4da85896bb289c81)