Bug#36365067 - EXPLAIN queries in MLE stored program causes

assertion failure

- Executing EXPLAIN/DESCRIBE statements from MLE SP using prepared
  statement execution causes a crash.
- To address this issue temporarily, the solution is to disable the
  cursor for such statements.
- The proper fix should be implemented in Bug#36332426.
- Additionally, include extra test cases to cover scenarios involving
  these statements.

Change-Id: Ibda9995a60ff2a74548342f0fda8f1c768726726

Author: Anushree Prakash B

sql/statement/statement.cc

@@ -473,6 +473,13 @@ bool Prepared_statement_handle::enable_cursor() {
          m_thd->server_status & SERVER_MORE_RESULTS_EXISTS);
 
   Sql_cmd *sql_cmd = m_stmt->m_lex->m_sql_cmd;
+
+  /*
+    Note: Temporary fix to disable cursor for EXPLAIN in prepared statement
+    till Bug#36332426 is resolved.
+  */
+  if (m_stmt->m_lex->is_explain()) return false;
+
   /*
     Enable cursors only when results are not directly relayed to the client and
     only command is suitable for cursors.