MDEV-6221 SQL_CALC_FOUND_ROWS yields wrong result again

replace another old "was there a filesort?" test with
a correct "did filesort calculate found_rows?" test.

mysql-test/r/select_found.result

@@ -315,3 +315,20 @@ select found_rows();
 found_rows()
 128
 drop table t1, t2;
+create table t1 (i1 int, v1 int, primary key(i1,v1));
+insert into t1 values (1,1),(2,2),(3,3);
+create table t2 (i2 int primary key, v2 int);
+insert into t2 values (1,5),(2,5),(3,10);
+select 1 as res from t1 left join t2 on i1 = i2 where v2 = 5 or v1 = 5 or v1 = 10 order by v1;
+res
+1
+1
+select sql_calc_found_rows 1 as res from t1 left join t2 on i1 = i2 where v2 = 5 or v1 = 5 or v1 = 10 order by v1 limit 1;
+select found_rows() as count;
+count
+2
+select sql_calc_found_rows 1 as res from t1 left join t2 on i1 = i2 where v2 = 5 order by v1 limit 1;
+select found_rows() as count;
+count
+2
+drop table t1, t2;

mysql-test/t/select_found.test

@@ -241,3 +241,19 @@ select found_rows();
 
 drop table t1, t2;
 
+#
+# MDEV-6221 SQL_CALC_FOUND_ROWS yields wrong result again
+#
+create table t1 (i1 int, v1 int, primary key(i1,v1));
+insert into t1 values (1,1),(2,2),(3,3);
+create table t2 (i2 int primary key, v2 int);
+insert into t2 values (1,5),(2,5),(3,10);
+select 1 as res from t1 left join t2 on i1 = i2 where v2 = 5 or v1 = 5 or v1 = 10 order by v1;
+--disable_result_log ONCE
+select sql_calc_found_rows 1 as res from t1 left join t2 on i1 = i2 where v2 = 5 or v1 = 5 or v1 = 10 order by v1 limit 1;
+select found_rows() as count;
+--disable_result_log ONCE
+select sql_calc_found_rows 1 as res from t1 left join t2 on i1 = i2 where v2 = 5 order by v1 limit 1;
+select found_rows() as count;
+drop table t1, t2;
+

sql/sql_select.cc

@@ -18724,8 +18724,7 @@ end_send(JOIN *join, JOIN_TAB *join_tab __attribute__((unused)),
 	  TABLE *table=jt->table;
 
           join->select_options ^= OPTION_FOUND_ROWS;
-	  if (table->sort.record_pointers ||
-	      (table->sort.io_cache && my_b_inited(table->sort.io_cache)))
+          if (join->filesort_found_rows)
 	  {
 	    /* Using filesort */
 	    join->send_records= table->sort.found_records;