rtr_pcur_getnext_from_path(): Remove a bogus condition.
The predicate lock should be acquired also on no match,
to ensure that the locking read will be repeatable.

This is based on the following fix in MySQL 5.7.24:

commit 365111c590082984dbae42e1d1da28ac3f7fb5bd
Author: Jimmy Yang <jimmy.yang@oracle.com>
Date:   Wed Jun 6 16:23:00 2018 -0700

    Fix Bug 27577612 - CONCURRENT SERIALIZABLE TRANSACTIONS CAN INSERT INTO
    AN AREA SELECTED FOR UPDATE
    Backport fix to mysql-5.7
Reviewed-by: Allen Lai <allen.lai@oracle.com>

No test case is added, because the MySQL 5.7 test case would pass
even when the fix is not present. We would need a test case that
only causes a locking conflict on the spatial index.