MDEV-25257 SEGV in fts_get_next_doc_id upon some INSERT

- InnoDB fails to create a fts cache while loading the innodb fts
table which is stored in system tablespace. InnoDB should create
the fts cache while loading FTS_DOC_ID column from system column.

mysql-test/suite/innodb_fts/r/fulltext.result

@@ -718,4 +718,18 @@ t1	CREATE TABLE `t1` (
   FULLTEXT KEY `a_2` (`a`)
 ) ENGINE=InnoDB DEFAULT CHARSET=latin1
 DROP TABLE t1;
+#
+# MDEV-25257 SEGV in fts_get_next_doc_id upon some INSERT
+#
+SET @save = @@global.innodb_file_per_table;
+SET @@global.innodb_file_per_table = 0;
+CREATE TABLE t1 (
+col_int INTEGER, col_text TEXT,
+col_int_g INTEGER GENERATED ALWAYS AS (col_int)
+) ENGINE = InnoDB ROW_FORMAT = Redundant ;
+ALTER TABLE t1 ADD FULLTEXT KEY `ftidx` ( col_text ) ;
+ALTER TABLE t1 DROP KEY `ftidx` ;
+INSERT INTO t1 (col_int, col_text) VALUES ( 1255, NULL);
+DROP TABLE t1;
+SET @@global.innodb_file_per_table = @save;
 # End of 10.3 tests

mysql-test/suite/innodb_fts/t/fulltext.test

@@ -741,4 +741,20 @@ ALTER TABLE t1 ADD FULLTEXT INDEX (a);
 SHOW CREATE TABLE t1;
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-25257 SEGV in fts_get_next_doc_id upon some INSERT
+--echo #
+SET @save = @@global.innodb_file_per_table;
+SET @@global.innodb_file_per_table = 0;
+
+CREATE TABLE t1 (
+   col_int INTEGER, col_text TEXT,
+   col_int_g INTEGER GENERATED ALWAYS AS (col_int)
+) ENGINE = InnoDB ROW_FORMAT = Redundant ;
+ALTER TABLE t1 ADD FULLTEXT KEY `ftidx` ( col_text ) ;
+ALTER TABLE t1 DROP KEY `ftidx` ;
+INSERT INTO t1 (col_int, col_text) VALUES ( 1255, NULL);
+DROP TABLE t1;
+SET @@global.innodb_file_per_table = @save;
+
 --echo # End of 10.3 tests

storage/innobase/dict/dict0load.cc

@@ -1851,6 +1851,7 @@ dict_load_columns(
 			the flag is set before the table is created. */
 			if (table->fts == NULL) {
 				table->fts = fts_create(table);
+				table->fts->cache = fts_cache_create(table);
 				fts_optimize_add_table(table);
 			}