MDEV-27924 page_zip_copy_recs() corrupts ROW_FORMAT=COMPRESSED block descriptor

In commit aaef2e1d (MDEV-27058)
we failed to introduce a special copy constructor that would
preserve the "page_zip_des_t::fix" field that only exists there
in order to avoid alignment loss on 64-bit systems.

page_zip_copy_recs(): Invoke the special copy constructor.

The block descriptor corruption causes assertion failures when
running ./mtr --suite=innodb_zip while InnoDB has been built
with UNIV_ZIP_COPY. Normally, calls to page_zip_copy_recs()
occur very rarely on page splits.

storage/innobase/include/page0types.h

 /*****************************************************************************
 
 Copyright (c) 1994, 2016, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2019, 2021, MariaDB Corporation.
+Copyright (c) 2019, 2022, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -119,6 +119,16 @@ struct page_zip_des_t
 		       - reinterpret_cast<char*>(this));
 	}
 
+	page_zip_des_t() = default;
+	page_zip_des_t(const page_zip_des_t&) = default;
+
+	/* Initialize everything except the member "fix". */
+	page_zip_des_t(const page_zip_des_t& old, bool) {
+		memcpy((void*) this, (void*) &old,
+		       reinterpret_cast<char*>(&fix)
+		       - reinterpret_cast<char*>(this));
+	}
+
 private:
 	friend buf_pool_t;
 	friend buf_page_t;

storage/innobase/page/page0zip.cc

@@ -2,7 +2,7 @@
 
 Copyright (c) 2005, 2016, Oracle and/or its affiliates. All Rights Reserved.
 Copyright (c) 2012, Facebook Inc.
-Copyright (c) 2014, 2021, MariaDB Corporation.
+Copyright (c) 2014, 2022, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -4562,7 +4562,7 @@ page_zip_copy_recs(
 	to the compressed data page. */
 	{
 		page_zip_t*	data = page_zip->data;
-		new (page_zip) page_zip_des_t(*src_zip);
+		new (page_zip) page_zip_des_t(*src_zip, false);
 		page_zip->data = data;
 	}
 	ut_ad(page_zip_get_trailer_len(page_zip, dict_index_is_clust(index))