MDEV-23897 SIGSEGV on commit with innodb_lock_schedule_algorithm=VATS

This regression for debug builds was introduced by
MDEV-23101 (commit 224c9504).

Due to MDEV-16664, the parameter
innodb_lock_schedule_algorithm=VATS
is not enabled by default.

The purpose of the added assertions was to enforce the invariant that
Galera replication cannot be enabled together with VATS due to MDEV-12837.
However, upon closer inspection, it is obvious that the variable 'lock'
may be assigned to the null pointer if no match is found in the
previous->hash list.

lock_grant_and_move_on_page(), lock_grant_and_move_on_rec():
Assert !lock->trx->is_wsrep() only after ensuring that lock
is not a null pointer.

mysql-test/suite/innodb/t/update-cascade.combinations

+[FCFS]
+--innodb-lock-schedule-algorithm=FCFS
+
+[VATS]
+--innodb-lock-schedule-algorithm=VATS

storage/innobase/lock/lock0lock.cc

@@ -2306,12 +2306,12 @@ lock_grant_and_move_on_page(ulint rec_fold, ulint space, ulint page_no)
 		lock = previous->hash;
 	}
 
-	ut_ad(!lock->trx->is_wsrep());
 	ut_ad(previous->hash == lock || previous == lock);
 	/* Grant locks if there are no conflicting locks ahead.
 	 Move granted locks to the head of the list. */
 	while (lock) {
 		/* If the lock is a wait lock on this page, and it does not need to wait. */
+		ut_ad(!lock->trx->is_wsrep());
 		if (lock_get_wait(lock)
 		    && lock->un_member.rec_lock.space == space
 		    && lock->un_member.rec_lock.page_no == page_no
@@ -4211,11 +4211,10 @@ lock_grant_and_move_on_rec(
 	    }
 		lock = previous->hash;
 	}
-	ut_ad(!lock->trx->is_wsrep());
 	/* Grant locks if there are no conflicting locks ahead.
 	 Move granted locks to the head of the list. */
-	for (;lock != NULL;) {
-
+	while (lock) {
+		ut_ad(!lock->trx->is_wsrep());
 		/* If the lock is a wait lock on this page, and it does not need to wait. */
 		if (lock->un_member.rec_lock.space == space
 			&& lock->un_member.rec_lock.page_no == page_no