Issue:
======
In JOIN::create_intermediate_table we free tmp table
descriptor because of some error while creating the tmp
table. But after freeing we failed to reset JOIN_TAB->table
entry. Further access of this invalid pointer resulted in
issue.

Solution:
=========
Reset JOIN_TAB->table. Also in JOIN::destroy call
free_tmp_table only if JOIN_TAB->table is set. This avoid
double free of temp tables.