In addtion, fixed a crash if the start position is greater than the
length of the string being searched.
Change-Id: I9bcda1131324bdfac6957018e91b3a36dd2dc3d6
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/118996
Tested-by: Jenkins
Reviewed-by: Andreas Heinisch <andreas.heinisch@yahoo.de>