Bug#22151233 MEMORY LEAKS WHEN DOING INSERT... UPDATE ... PREPARED STATEMENTS

Problem: memory leaks when doing INSERT... UPDATE ... prepared statements.
Regression source is patch for
    Bug#21908206 MEMORY LEAK ON WINDOWS WHEN SELECT FROM VIEW IN SUBQUERY
Which fixed a regression caused by
    Bug#13901905 - CRASH: INSERT ON DUPLICATE KEY UPDATE READS FREED MEMORY

The patch for Bug#21908206 fixed a leak for LEX objects that were not
properly destroyed.

Solution: clear the std::map for LEX objects thar *are* destroyed.

Author: Tor Didriksen

sql/sql_lex.cc

@@ -3528,6 +3528,7 @@ LEX::LEX()
    plugins(PSI_NOT_INSTRUMENTED),
    insert_update_values_map(NULL),
    option_type(OPT_DEFAULT),
+   sphead(NULL),
    is_set_password_sql(false),
    // Initialize here to avoid uninitialized variable warnings.
    contains_plaintext_password(false),

sql/sql_prepare.cc

@@ -3105,8 +3105,10 @@ Prepared_statement::~Prepared_statement()
   free_items();
   if (lex)
   {
+    DBUG_ASSERT(lex->sphead == NULL);
+    lex_end(lex);
     delete lex->result;
-    delete (st_lex_local *) lex;
+    delete (st_lex_local *) lex;                // TRASH memory
   }
   free_root(&main_mem_root, MYF(0));
   DBUG_VOID_RETURN;