This also fixes some issues with
MDEV-23730 s3.replication_partition 'innodb,mix' segv

The problem was that mysql_change_partitions() closes all handler files
in case of error, which was not properly reflected in
fast_alter_partition_table(). This caused handle_alter_part_error() to
try to close already closed tables, which caused the crash.

Fixed fast_alter_partion_table() to reflect when tables are opened.
I also fixed that ha_partition::change_partitions() resets m_new_file in
case of errors.
Either of the above changes fixes the issue, but both are needed to ensure
that the code works as expected.