A fix and a test case for Bug#56540 "Exception (crash) in

sql_show.cc during rqg_info_schema test on Windows".

Ensure we do not access freed memory when filling
information_schema.views when one of the views
could not be properly opened.



mysql-test/r/information_schema.result:
  Update results - a fix for Bug#56540.
mysql-test/t/information_schema.test:
  Add a test case for Bug#56540
sql/sql_base.cc:
  Push an error into the Diagnostics area
  when we return an error.
  This directs get_all_tables() to the execution
  branch which doesn't involve 'process_table()'
  when no table/view was opened.
sql/sql_show.cc:
  Do not try to access underlying table fields
  when opening of a view failed. The underlying
  table is closed in that case, and accessing
  its fields may lead to dereferencing a damaged 
  pointer.

mysql-test/t/information_schema.test

@@ -1555,3 +1555,56 @@ WHERE COLUMNS.TABLE_SCHEMA = 'test'
 AND COLUMNS.TABLE_NAME = 't1';
 
 
+--echo #
+--echo # A test case for Bug#56540 "Exception (crash) in sql_show.cc
+--echo # during rqg_info_schema test on Windows"
+--echo # Ensure that we never access memory of a closed table,
+--echo # in particular, never access table->field[] array.
+--echo # Before the fix, the below test case, produced
+--echo # valgrind errors.
+--echo #
+
+--disable_warnings
+drop table if exists t1;
+drop view if exists v1;
+--enable_warnings
+
+create table t1 (a int, b int);
+create view v1 as select t1.a, t1.b from t1;
+alter table t1 change b c int;
+lock table t1 read;
+connect(con1, localhost, root,,);
+--echo # --> connection con1
+connection con1;
+send flush tables;
+--echo # --> connection default
+connection default;
+let $wait_condition=
+  select count(*) = 1 from information_schema.processlist
+    where state = "Waiting for table flush" and
+          info = "flush tables";
+--source include/wait_condition.inc
+--vertical_results
+select * from information_schema.views;
+--horizontal_results
+unlock tables;
+
+--echo #
+--echo # Cleanup.
+--echo #
+
+--echo # --> connection con1
+connection con1;
+--echo # Reaping 'flush tables'
+reap;
+disconnect con1;
+--source include/wait_until_disconnected.inc
+--echo # --> connection default
+connection default;
+drop table t1;
+drop view v1;
+
+
+--echo #
+--echo # End of 5.5 tests
+--echo #