Bug#44653: Server crash noticed when executing random queries with partitions.

When opening a table, it is imperative that the flag
TABLE::auto_increment_field_not_null be false. But if an error occured during
the creation of a table (e.g. the table exists already) with an auto_increment
column and a BEFORE trigger that used the INSERT ... SELECT construct, the
flag was not reset until after error checking. Thus if an error occured,
select_insert::send_data() returned immediately and it was not reset (see * in
pseudocode below).  Crash happened if the table was opened again. Fixed by
resetting the flag after error checking.

nested-loops_join():
  for each row in SELECT table {
    select_insert::send_data():
      if a values is supplied for AUTO_INCREMENT column
         table->auto_increment_field_not_null= TRUE
       else
         table->auto_increment_field_not_null= FALSE
       if (error)
         return 1; *
       if (table->auto_increment_field_not_null == FALSE)
         ...
       table->auto_increment_field_not_null == FALSE 
  }
<-- table returned to table cache and later retrieved by open_table: 
open_table():
  assert(table->auto_increment_field_not_null)


mysql-test/r/trigger.result:
  Bug#44653: Test result
mysql-test/t/trigger.test:
  Bug#44653: Test case
sql/sql_insert.cc:
  Bug#44653: Fix: Make sure to unset this field before returning in case of error