fdo#74474: sw: fix Label wizard document creation (2 in 1)

Infinite loop in InsertLabEnvText() due to wrong handling of starting '<'.

(regression from fa469b2e00d83459faebe4c1fcb3ea1aac5fb20d)

(cherry picked from commit 7e61bfe813347949307cdf2876ead3cc42e4cd7b)

The function ReplacePoint() was changed to return a value but not all
call sites were adapted.
(regression from 263153842741d7ce21cc0bf1c5296a55a1138024)

(cherry picked from commit 9dbe5a576330b7fadd8838249d07aafe548a4ee2)

Change-Id: I33efd9ce61611e025dfc76047187826aa0f8dd84
Reviewed-on: https://gerrit.libreoffice.org/7931
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>