MDEV-26826 fixup: ROW_FORMAT=COMPRESSED may corrupt buf_pool.page_hash

In commit c091a0b we removed
the use of the HASH_ macros for inserting into
buf_pool.page_hash, or accessing buf_page_t::hash.

However, the binary buddy allocator for block->page.zip.data would
still use the HASH_ macros. HASH_INSERT and not HASH_DELETE would reset
the next-block pointer to the null pointer. Our replacement of
HASH_DELETE() will reset the next-block pointer, and the replacement of
HASH_INSERT() assumes that the pointer is the null pointer.

buf_LRU_block_free_non_file_page(): Assert that the next-block pointer
is the null pointer.

buf_buddy_block_free(): Reset the pointer before invoking
buf_LRU_block_free_non_file_page(). Without this, the added
assertion would fail in the test encryption.innochecksum.

storage/innobase/buf/buf0buddy.cc

@@ -362,6 +362,7 @@ buf_buddy_block_free(void* buf)
 	ut_ad(bpage->in_zip_hash);
 	ut_d(bpage->in_zip_hash = false);
 	HASH_DELETE(buf_page_t, hash, &buf_pool.zip_hash, fold, bpage);
+	bpage->hash = nullptr;
 
 	ut_d(memset(buf, 0, srv_page_size));
 	MEM_UNDEFINED(buf, srv_page_size);

storage/innobase/buf/buf0buf.cc

@@ -219,7 +219,7 @@ buf_pool.LRU.
 
 The chains of free memory blocks (buf_pool.zip_free[]) are used by
 the buddy allocator (buf0buddy.cc) to keep track of currently unused
-memory blocks of size sizeof(buf_page_t)..srv_page_size / 2.  These
+memory blocks of size UNIV_PAGE_SIZE_MIN..srv_page_size / 2.  These
 blocks are inside the srv_page_size-sized memory blocks of type
 BUF_BLOCK_MEMORY that the buddy allocator requests from the buffer
 pool.  The buddy allocator is solely used for allocating control

storage/innobase/buf/buf0lru.cc

@@ -1010,6 +1010,7 @@ buf_LRU_block_free_non_file_page(
 	ut_ad(!block->page.in_free_list);
 	ut_ad(!block->page.oldest_modification());
 	ut_ad(!block->page.in_LRU_list);
+	ut_ad(!block->page.hash);
 
 	block->page.set_state(BUF_BLOCK_NOT_USED);