Instead of simply doing a match against a string S at offset O > 0
(and checking the result), test that the results never change when matching
against the substring starting at (O - i) at offset i, 0 <= i <= O.
Change-Id: Ib7fd648ca0a36b93d145267ebfb792c46ca4e4f5
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>