MDEV-18025: Detect corrupted innodb_page_compression=zlib pages

In MDEV-13103, I made a mistake in the error handling of
page_compressed=1 decryption when the default
innodb_compression_algorithm=zlib is used.
Due to this mistake, with certain versions of zlib,
MariaDB would fail to detect a corrupted page.

The problem was uncovered by the following tests:
mariabackup.unencrypted_page_compressed
mariabackup.encrypted_page_compressed

Author: dr-m

storage/innobase/fil/fil0pagecompress.cc

@@ -341,14 +341,14 @@ UNIV_INTERN ulint fil_page_decompress(byte* tmp_buf, byte* buf)
 	case PAGE_ZLIB_ALGORITHM:
 		{
 			uLong len = srv_page_size;
-			if (Z_OK != uncompress(tmp_buf, &len,
+			if (Z_OK == uncompress(tmp_buf, &len,
 					       buf + header_len,
 					       uLong(actual_size))
-			    && len != srv_page_size) {
-				return 0;
+			    && len == srv_page_size) {
+				break;
 			}
 		}
-		break;
+		return 0;
 #ifdef HAVE_LZ4
 	case PAGE_LZ4_ALGORITHM:
 		if (LZ4_decompress_safe(reinterpret_cast<const char*>(buf)

storage/xtradb/fil/fil0pagecompress.cc

@@ -341,14 +341,14 @@ UNIV_INTERN ulint fil_page_decompress(byte* tmp_buf, byte* buf)
 	case PAGE_ZLIB_ALGORITHM:
 		{
 			uLong len = srv_page_size;
-			if (Z_OK != uncompress(tmp_buf, &len,
+			if (Z_OK == uncompress(tmp_buf, &len,
 					       buf + header_len,
 					       uLong(actual_size))
-			    && len != srv_page_size) {
-				return 0;
+			    && len == srv_page_size) {
+				break;
 			}
 		}
-		break;
+		return 0;
 #ifdef HAVE_LZ4
 	case PAGE_LZ4_ALGORITHM:
 		if (LZ4_decompress_safe(reinterpret_cast<const char*>(buf)