MDEV-10679 Crash in performance schema and partitioning with discovery

Crash happened because in discover, table->work_part_info was not properly
reset before execution.
Fixed by resetting before calling execute alter table, create table or
mysql_create_frm_image.

sql/sql_alter.cc

@@ -262,8 +262,8 @@ bool Sql_cmd_alter_table::execute(THD *thd)
 
         - For temporary MERGE tables we do not track if their child tables are
           base or temporary. As result we can't guarantee that privilege check
-          which was done in presence of temporary child will stay relevant later
-          as this temporary table might be removed.
+          which was done in presence of temporary child will stay relevant
+          later as this temporary table might be removed.
 
       If SELECT_ACL | UPDATE_ACL | DELETE_ACL privileges were not checked for
       the underlying *base* tables, it would create a security breach as in
@@ -303,6 +303,7 @@ bool Sql_cmd_alter_table::execute(THD *thd)
   create_info.data_file_name= create_info.index_file_name= NULL;
 
   thd->enable_slow_log= opt_log_slow_admin_statements;
+  thd->work_part_info= 0;
 
 #ifdef WITH_WSREP
   TABLE *find_temporary_table(THD *thd, const TABLE_LIST *tl);

sql/sql_parse.cc

@@ -2475,10 +2475,6 @@ mysql_execute_command(THD *thd)
 #endif
   DBUG_ENTER("mysql_execute_command");
 
-#ifdef WITH_PARTITION_STORAGE_ENGINE
-  thd->work_part_info= 0;
-#endif
-
   DBUG_ASSERT(thd->transaction.stmt.is_empty() || thd->in_sub_stmt);
   /*
     Each statement or replication event which might produce deadlock
@@ -3318,6 +3314,7 @@ mysql_execute_command(THD *thd)
       create_info.add(DDL_options_st::OPT_OR_REPLACE_SLAVE_GENERATED);
     }
 
+    thd->work_part_info= 0;
 #ifdef WITH_PARTITION_STORAGE_ENGINE
     {
       partition_info *part_info= thd->lex->part_info;

sql/sql_table.cc

@@ -6057,6 +6057,7 @@ remove_key:
     }
   }
   
+  DBUG_ASSERT(thd->work_part_info == 0);
 #ifdef WITH_PARTITION_STORAGE_ENGINE
   partition_info *tab_part_info= table->part_info;
   thd->work_part_info= thd->lex->part_info;
@@ -8411,6 +8412,8 @@ bool mysql_alter_table(THD *thd,char *new_db, char *new_name,
 {
   DBUG_ENTER("mysql_alter_table");
 
+  thd->work_part_info= 0;                       // Used by partitioning
+
   /*
     Check if we attempt to alter mysql.slow_log or
     mysql.general_log table and return an error if

sql/table.cc

@@ -2233,6 +2233,7 @@ int TABLE_SHARE::init_from_sql_statement_string(THD *thd, bool write,
     goto ret;
 
   thd->lex->create_info.db_type= hton;
+  thd->work_part_info= 0;                       // For partitioning
 
   if (tabledef_version.str)
     thd->lex->create_info.tabledef_version= tabledef_version;