When acquiring SNW/SNRW/X MDL lock DDL/admin statements may abort pending
thr lock in concurrent connection with open HANDLER (or delayed insert
thread).

This may lead to a race condition when table->alias is accessed
concurrently by such threads. Either assertion failure or memory leak
is a practical consequence of this race condition.

Specifically HANDLER is opening a table and issuing alias.copy(), while
DDL executing get_lock_data()/alias.c_ptr()/realloc()/realloc_raw().

Fixed by perforimg table->init() before it is published via
thd->open_tables.