MDEV-37447: Race condition between buf_pool_t::shrink() and page_guess()

buf_pool_t::shrink(): When relocating a buffer page, invalidate
the page identifier of the original page so that buf_pool_t::page_guess()
will not accidentally match it.

Before commit b692342 (MDEV-29445)
introduced buf_pool_t::page_guess(), the validity of block descriptor
pointers was checked by buf_pool_t::is_uncompressed(const buf_block_t*).
Therefore, any block descriptors that used to be part of a larger buffer
pool would not be accessed at all.

This race condition is very hard to reproduce. To reproduce it,
an optimistic btr_pcur_t::restore_position() or similar will have to
be invoked on a block that has been relocated by buf_pool_t::shrink()
and that had not meanwhile been replaced with another page with a
different identifier.

Reviewed by: Vladislav Lesin

Author: dr-m

storage/innobase/buf/buf0buf.cc

@@ -1781,6 +1781,7 @@ ATTRIBUTE_COLD buf_pool_t::shrink_status buf_pool_t::shrink(size_t size)
     /* relocate page_hash */
     ut_ad(b == page_hash.get(id, chain));
     page_hash.replace(chain, b, &block->page);
+    b->id_.set_corrupted();
 
     if (b->zip.data)
     {