Bug#17142 Crash if create with encoded name

upgrade.result, upgrade.test:
  Adding test case.
table.cc:
  Don't try to open a table with old-formatted name,
  if the table name contains "@" character.
  This is to avoid mixing two different names to each other.
  Thanks Monty for suggesting this fix.

mysql-test/r/upgrade.result

@@ -41,3 +41,19 @@ t1
 t-1
 drop database `mysqltest1`;
 drop database `mysqltest-1`;
+drop table if exists `txu@0023P@0023p1`;
+drop table if exists `txu#P#p1`;
+create table `txu#P#p1` (s1 int);
+insert into `txu#P#p1` values (1);
+select * from `txu@0023P@0023p1`;
+ERROR 42S02: Table 'test.txu@0023P@0023p1' doesn't exist
+create table `txu@0023P@0023p1` (s1 int);
+insert into `txu@0023P@0023p1` values (2);
+select * from `txu@0023P@0023p1`;
+s1
+2
+select * from `txu#P#p1`;
+s1
+1
+drop table `txu@0023P@0023p1`;
+drop table `txu#P#p1`;

mysql-test/t/upgrade.test

@@ -29,3 +29,21 @@ show tables in `mysqltest1`;
 show tables in `mysqltest-1`;
 drop database `mysqltest1`;
 drop database `mysqltest-1`;
+
+#
+# Bug#17142: Crash if create with encoded name
+#
+--disable_warnings
+drop table if exists `txu@0023P@0023p1`;
+drop table if exists `txu#P#p1`;
+--enable_warnings
+create table `txu#P#p1` (s1 int);
+insert into `txu#P#p1` values (1);
+--error 1146
+select * from `txu@0023P@0023p1`;
+create table `txu@0023P@0023p1` (s1 int);
+insert into `txu@0023P@0023p1` values (2);
+select * from `txu@0023P@0023p1`;
+select * from `txu#P#p1`;
+drop table `txu@0023P@0023p1`;
+drop table `txu#P#p1`;

sql/table.cc

@@ -298,6 +298,9 @@ int open_table_def(THD *thd, TABLE_SHARE *share, uint db_flags)
   strxmov(path, share->normalized_path.str, reg_ext, NullS);
   if ((file= my_open(path, O_RDONLY | O_SHARE, MYF(0))) < 0)
   {
+    if (strchr(share->table_name.str, '@'))
+      goto err_not_open;
+
     /* Try unecoded 5.0 name */
     uint length;
     strxnmov(path, sizeof(path)-1,