row_metadata_to_tuple(), row_rec_to_index_entry_impl():
Add the parameter "pad" to determine whether
the tuple should be padded to the index fields (on ALTER TABLE it should),
or whether it should remain at its original size (on rollback).

trx_undo_page_report_modify(): Avoid out-of-bounds access to record fields.

row_quiesce_write_index_fields(): Do not crash when the table contains
an instantly dropped column.