The test case encryption.innodb_encrypt_freed was failing in
MemorySanitizer builds.

recv_recover_page(): Mark non-recovered pages as freed.

fil_crypt_rotate_page(): Before comparing the block->frame contents,
check if the block was marked as freed.

Other places: Whenever using BUF_GET_POSSIBLY_FREED, check the
block->page.status before accessing the page frame.

(Both uses of BUF_GET_IF_IN_POOL should be correct now.)