MDEV-7408: Cannot use a table containing special chars for InnoDB stopwords

Added test case. No actual bug found.

mysql-test/suite/innodb/r/innodb-mdev-7408.result

+select @@global.innodb_ft_server_stopword_table;
+@@global.innodb_ft_server_stopword_table
+NULL
+CREATE TABLE `stop_it-IT` ENGINE = InnoDB SELECT * FROM information_schema.INNODB_FT_DEFAULT_STOPWORD;
+SET @@global.innodb_ft_server_stopword_table = 'test/stop_it-IT';
+ERROR 42000: Variable 'innodb_ft_server_stopword_table' can't be set to the value of 'test/stop_it-IT'
+SET @@global.innodb_ft_server_stopword_table = 'test/stop_it@002dIT';
+drop table `stop_it-IT`;
+CREATE TABLE stop_it ENGINE = InnoDB SELECT * FROM information_schema.INNODB_FT_DEFAULT_STOPWORD;
+SET @@global.innodb_ft_server_stopword_table = 'test/stop_it';
+SET @@global.innodb_ft_server_stopword_table = NULL;
+drop table stop_it;

mysql-test/suite/innodb/t/innodb-mdev-7408.opt

+--innodb_ft_default_stopword
+

mysql-test/suite/innodb/t/innodb-mdev-7408.test

+--source include/have_innodb.inc
+
+select @@global.innodb_ft_server_stopword_table;
+CREATE TABLE `stop_it-IT` ENGINE = InnoDB SELECT * FROM information_schema.INNODB_FT_DEFAULT_STOPWORD;
+--error 1231
+SET @@global.innodb_ft_server_stopword_table = 'test/stop_it-IT';
+SET @@global.innodb_ft_server_stopword_table = 'test/stop_it@002dIT';
+drop table `stop_it-IT`;
+
+CREATE TABLE stop_it ENGINE = InnoDB SELECT * FROM information_schema.INNODB_FT_DEFAULT_STOPWORD;
+SET @@global.innodb_ft_server_stopword_table = 'test/stop_it';
+
+SET @@global.innodb_ft_server_stopword_table = NULL;
+
+drop table stop_it;