buf_flush_init_for_writing(): Calculate the checksum with the actual zip_size.

buf_calc_zblob_page_checksum(): Skip the field FIL_PAGE_SPACE_OR_CHKSUM.

trx_sys_doublewrite_init_or_restore_page(): Use the actual zip_size.

page_cur_insert_rec_low(): If page_zip_alloc() fails, try compressing the
whole page afterwards.