Assertion `table->key_read == 0' failed.

The problem was that key_read on a table in a sub-select was not
properly reset. That happens because the code responsible for that
is copy&pasted all around the server. In some place, it was obviously
forgotten to be pasted.

The fix is to reset key_read properly.


mysql-test/r/key.result:
  Update result file.
mysql-test/t/key.test:
  A test case for BUG#31148: bool close_thread_table(THD*, TABLE**):
  Assertion `table->key_read == 0' failed.
sql/sql_select.cc:
  Reset key_read before closing index.