MDEV-22639 Assertion failed in ha_check_overlaps upon multi-table update

After Sergei's cleanup this assertion is not actual anymore -- we can't
predict if the handler was used for lookup, especially in multi-update
scenario.

`position(old_data)` is made earlier in `ha_check_overlaps`, therefore it
is guaranteed that we compare right refs.

mysql-test/suite/period/r/overlaps.result

@@ -329,4 +329,12 @@ unique(f, p without overlaps));
 insert into t1 values (0,'2026-02-12','2036-09-16'),
 (null,'2025-03-09','2032-12-05');
 update ignore t join t1 set f = a;
+# MDEV-22639  Assertion `inited != NONE' failed in
+# handler::ha_check_overlaps upon multi-table update
+create or replace table t (f int, s date, e date, period for p(s,e),
+unique(f, p without overlaps)) engine=myisam;
+insert into t values (1,'1988-08-25','2024-03-06');
+create or replace table t1 (a int) engine=myisam;
+insert into t1 values (1),(2);
+update t join t1 set s = '2020-01-01';
 drop table t, t1;

mysql-test/suite/period/t/overlaps.test

@@ -313,5 +313,15 @@ insert into t1 values (0,'2026-02-12','2036-09-16'),
 
 update ignore t join t1 set f = a;
 
+--echo # MDEV-22639  Assertion `inited != NONE' failed in
+--echo # handler::ha_check_overlaps upon multi-table update
+
+create or replace table t (f int, s date, e date, period for p(s,e),
+                           unique(f, p without overlaps)) engine=myisam;
+insert into t values (1,'1988-08-25','2024-03-06');
+create or replace table t1 (a int) engine=myisam;
+insert into t1 values (1),(2);
+
+update t join t1 set s = '2020-01-01';
 
 drop table t, t1;

sql/handler.cc

@@ -6947,7 +6947,7 @@ int handler::ha_check_overlaps(const uchar *old_data, const uchar* new_data)
   uchar *record_buffer= lookup_buffer + table_share->max_unique_length
                                       + table_share->null_fields;
 
-  // Needs to compare record refs later is old_row_found()
+  // Needed to compare record refs later
   if (is_update)
     position(old_data);
 
@@ -7003,12 +7003,8 @@ int handler::ha_check_overlaps(const uchar *old_data, const uchar* new_data)
       /* In case of update it could happen that the nearest neighbour is
          a record we are updating. It means, that there are no overlaps
          from this side.
-
-         An assumption is made that during update we always have the last
-         fetched row in old_data. Therefore, comparing ref's is enough
       */
       DBUG_ASSERT(lookup_handler != this);
-      DBUG_ASSERT(inited != NONE);
       DBUG_ASSERT(ref_length == lookup_handler->ref_length);
 
       lookup_handler->position(record_buffer);