MDEV-20383 Use of uninitialized value in Datafile::find_space_id() for ROW_FORMAT=COMPRESSED

Datafile::find_space_id(): Fix a regression that was introduced
in c0f47a4a for MDEV-12026.
Because the function buf_page_is_corrupted() now determines
the physical page size from the fsp_flags, our buffer size must
agree with the fsp_flags.

buf_page_is_corrupted(): Use the correct accessor
fil_space_t::zip_size() for convering the tablespace flags.
ROW_FORMAT=COMPRESSED files never use innodb_checksum_algorithm=full_crc32.

storage/innobase/buf/buf0buf.cc

@@ -1068,14 +1068,8 @@ buf_page_is_corrupted(
 	size_t		checksum_field2 = 0;
 	uint32_t	crc32 = 0;
 	bool		crc32_inited = false;
-	ulint		zip_size = 0;
 	bool		crc32_chksum = false;
-
-	zip_size = FSP_FLAGS_GET_ZIP_SSIZE(fsp_flags);
-	if (zip_size) {
-		zip_size = (UNIV_ZIP_SIZE_MIN >> 1) << zip_size;
-	}
-
+	const ulint zip_size = fil_space_t::zip_size(fsp_flags);
 	ulint page_type = mach_read_from_2(read_buf + FIL_PAGE_TYPE);
 
 	/* We can trust page type if page compression is set on tablespace

storage/innobase/fsp/fsp0file.cc

@@ -699,7 +699,8 @@ Datafile::find_space_id()
 
 			/* For noncompressed pages, the page size must be
 			equal to srv_page_size. */
-			if (page_size == srv_page_size) {
+			if (page_size == srv_page_size
+			    && !fil_space_t::zip_size(fsp_flags)) {
 				noncompressed_ok = !buf_page_is_corrupted(
 					false, page, fsp_flags);
 			}
@@ -707,7 +708,7 @@ Datafile::find_space_id()
 			bool	compressed_ok = false;
 
 			if (srv_page_size <= UNIV_PAGE_SIZE_DEF
-			    && page_size <= srv_page_size) {
+			    && page_size == fil_space_t::zip_size(fsp_flags)) {
 				compressed_ok = !buf_page_is_corrupted(
 					false, page, fsp_flags);
 			}