rec_convert_dtuple_to_rec_old(): Initialize the record in order to avoid
bogus Valgrind warnings about the ut_ad() in mach_write_to_1() and
mach_write_to_2().

page_zip_compress(), page_zip_write_rec(), page_zip_write_blob_ptr():
Replace ut_ad(page_validate(...)) with ut_ad(page_simple_validate_new(...)),
because otherwise crash recovery would fail.