fdo#73162: sw: un-break index entries that contain text separators

SwFormTokensHelper::SearchNextToken() does some check that the ">" token
terminator is not inside a pair of TOX_STYLE_DELIMITER; this check was
broken by commit f4fd558ac9d61fe06aa0f56d829916ef9e5ee7b9 and finds a
">" outside of TOX_STYLE_DELIMITER bracketing.

Change-Id: Ia8587d496999c561f57fd6f107ed8b9d1e3838d4
(cherry picked from commit c87f146a0cec31f080386d646bfb786ed6200280)
Reviewed-on: https://gerrit.libreoffice.org/7439
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>