MDEV-25070 SIGSEGV in fts_create_in_mem_aux_table

InnoDB set the space in dict_table_t as NULL when table
is discarded. So InnoDB shouldn't use the space present
in table to detect whether the given tablespace is
temporary tablespace.

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

@@ -689,3 +689,19 @@ FTS_DOC_ID	t
 2	foo bar
 3	foo
 DROP TABLE t;
+#
+# MDEV-25070 SIGSEGV in fts_create_in_mem_aux_table
+# 
+CREATE TABLE t1 (a CHAR, FULLTEXT KEY(a)) ENGINE=InnoDB;
+ALTER TABLE t1 DISCARD TABLESPACE;
+ALTER TABLE t1 ADD FULLTEXT INDEX (a);
+Warnings:
+Warning	1814	Tablespace has been discarded for table `t1`
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` char(1) DEFAULT NULL,
+  FULLTEXT KEY `a` (`a`),
+  FULLTEXT KEY `a_2` (`a`)
+) ENGINE=InnoDB DEFAULT CHARSET=latin1
+DROP TABLE t1;

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

@@ -717,3 +717,12 @@ while ($N)
 }
 
 DROP TABLE t;
+
+--echo #
+--echo # MDEV-25070 SIGSEGV in fts_create_in_mem_aux_table
+--echo #
+CREATE TABLE t1 (a CHAR, FULLTEXT KEY(a)) ENGINE=InnoDB;
+ALTER TABLE t1 DISCARD TABLESPACE;
+ALTER TABLE t1 ADD FULLTEXT INDEX (a);
+SHOW CREATE TABLE t1;
+DROP TABLE t1;

storage/innobase/fts/fts0fts.cc

@@ -1730,7 +1730,7 @@ fts_create_in_mem_aux_table(
 	dict_table_t*	new_table = dict_mem_table_create(
 		aux_table_name, NULL, n_cols, 0, table->flags,
 		table->space_id == TRX_SYS_SPACE
-		? 0 : table->space->purpose == FIL_TYPE_TEMPORARY
+		? 0 : table->space_id == SRV_TMP_SPACE_ID
 		? DICT_TF2_TEMPORARY : DICT_TF2_USE_FILE_PER_TABLE);
 
 	if (DICT_TF_HAS_DATA_DIR(table->flags)) {