dict_create_index_tree_in_mem(): Remove dead code

In InnoDB, CREATE TEMPORARY TABLE does not allow FULLTEXT INDEX.
Replace a condition with a debug assertion, and add a test.

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

+CREATE TEMPORARY TABLE articles (
+id INT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY,
+title VARCHAR(200),
+body TEXT,
+FULLTEXT (title,body)
+) ENGINE=InnoDB;
+ERROR HY000: Cannot create FULLTEXT index on temporary InnoDB table
 CREATE TABLE articles (
 id INT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY,
 title VARCHAR(200),

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

@@ -3,6 +3,14 @@
 -- source include/have_innodb.inc
 
 # Create FTS table
+--error ER_INNODB_NO_FT_TEMP_TABLE
+CREATE TEMPORARY TABLE articles (
+	id INT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY,
+	title VARCHAR(200),
+	body TEXT,
+	FULLTEXT (title,body)
+	) ENGINE=InnoDB;
+
 CREATE TABLE articles (
 	id INT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY,
 	title VARCHAR(200),

storage/innobase/dict/dict0crea.cc

@@ -943,14 +943,10 @@ dict_create_index_tree_in_mem(
 	const trx_t*	trx)	/*!< in: InnoDB transaction handle */
 {
 	mtr_t		mtr;
-	ulint		page_no = FIL_NULL;
+	ulint		page_no;
 
 	ut_ad(mutex_own(&dict_sys->mutex));
-
-	if (index->type == DICT_FTS) {
-		/* FTS index does not need an index tree */
-		return(DB_SUCCESS);
-	}
+	ut_ad(!(index->type & DICT_FTS));
 
 	mtr_start(&mtr);
 	mtr_set_log_mode(&mtr, MTR_LOG_NO_REDO);