When swapping out heap I_S tables to disk, this is done after plan refinement.
Thus, READ_RECORD::file will still point to the (deleted) heap handler at start
of execution. This causes segmentation fault if join buffering is used and the 
query is a star query where the result is found to be empty before accessing
some table. In this case that table has not been initialized (i.e. had its 
READ_RECORD re-initialized) before the cleanup routine tries to close the handler.
Fixed by updating READ_RECORD::file when changing handler.


mysql-test/r/information_schema.result:
  Bug#34529: Test result.
mysql-test/t/information_schema.test:
  Bug#34529: Test case.
sql/sql_show.cc:
  Bug#34529: The fix.