MDEV-19695 Import tablespace doesn't work with ROW_FORMAT=COMPRESSED encrypted tablespace

Problem:
=======
fil_iterate() writes imported tablespace page0 as it is to discarded
tablespace. Space id wasn't even changed. While opening the tablespace,
tablespace fails with space id mismatch error.

Fix:
====
fil_iterate() copies the page0 with discarded space id to imported
tablespace.

mysql-test/suite/encryption/r/compressed_import_tablespace.result

+CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY, a VARCHAR(255)) ENGINE=InnoDB ROW_FORMAT=COMPRESSED ENCRYPTED=YES;
+INSERT INTO t1 VALUES(1, repeat('Nesamani', 10));
+SELECT COUNT(*) FROM t1;
+COUNT(*)
+1
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `id` int(11) NOT NULL,
+  `a` varchar(255) DEFAULT NULL,
+  PRIMARY KEY (`id`)
+) ENGINE=InnoDB DEFAULT CHARSET=latin1 ROW_FORMAT=COMPRESSED `ENCRYPTED`=YES
+# Wait max 10 min for key encryption threads to encrypt all spaces
+t1.frm
+t1.ibd
+FLUSH TABLES t1 FOR EXPORT;
+backup: t1
+t1.cfg
+t1.frm
+t1.ibd
+UNLOCK TABLES;
+DROP TABLE t1;
+CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY, a VARCHAR(255)) ENGINE=InnoDB ROW_FORMAT=COMPRESSED ENCRYPTED=YES;
+ALTER TABLE t1 DISCARD TABLESPACE;
+restore: t1 .ibd and .cfg files
+ALTER TABLE t1 IMPORT TABLESPACE;
+SELECT COUNT(*) FROM t1;
+COUNT(*)
+1
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `id` int(11) NOT NULL,
+  `a` varchar(255) DEFAULT NULL,
+  PRIMARY KEY (`id`)
+) ENGINE=InnoDB DEFAULT CHARSET=latin1 ROW_FORMAT=COMPRESSED `ENCRYPTED`=YES
+DROP TABLE t1;

mysql-test/suite/encryption/t/compressed_import_tablespace.opt

+--innodb-encrypt-tables=ON
+--innodb-encryption-threads=4
+--innodb-tablespaces-encryption

mysql-test/suite/encryption/t/compressed_import_tablespace.test

+-- source include/have_innodb.inc
+-- source include/have_example_key_management_plugin.inc
+-- source include/not_valgrind.inc
+-- source include/not_embedded.inc
+
+let MYSQLD_DATADIR = `SELECT @@datadir`;
+--let t1_IBD = $MYSQLD_DATADIR/test/t1.ibd
+CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY, a VARCHAR(255)) ENGINE=InnoDB ROW_FORMAT=COMPRESSED ENCRYPTED=YES;
+INSERT INTO t1 VALUES(1, repeat('Nesamani', 10));
+
+SELECT COUNT(*) FROM t1;
+SHOW CREATE TABLE t1;
+
+--echo # Wait max 10 min for key encryption threads to encrypt all spaces
+--let $wait_timeout= 600
+--let $wait_condition=SELECT COUNT(*) = 0 FROM INFORMATION_SCHEMA.INNODB_TABLESPACES_ENCRYPTION WHERE MIN_KEY_VERSION = 0 AND ROTATING_OR_FLUSHING <> 0
+--source include/wait_condition.inc
+
+--source include/shutdown_mysqld.inc
+
+--source include/start_mysqld.inc
+let MYSQLD_DATADIR =`SELECT @@datadir`;
+
+--list_files $MYSQLD_DATADIR/test
+FLUSH TABLES t1 FOR EXPORT;
+perl;
+do "$ENV{MTR_SUITE_DIR}/include/innodb-util.pl";
+ib_backup_tablespaces("test", "t1");
+EOF
+--list_files $MYSQLD_DATADIR/test
+UNLOCK TABLES;
+DROP TABLE t1;
+
+CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY, a VARCHAR(255)) ENGINE=InnoDB ROW_FORMAT=COMPRESSED ENCRYPTED=YES;
+ALTER TABLE t1 DISCARD TABLESPACE;
+perl;
+do "$ENV{MTR_SUITE_DIR}/include/innodb-util.pl";
+ib_discard_tablespaces("test", "t1");
+ib_restore_tablespaces("test", "t1");
+EOF
+
+ALTER TABLE t1 IMPORT TABLESPACE;
+
+SELECT COUNT(*) FROM t1;
+SHOW CREATE TABLE t1;
+DROP TABLE t1;

storage/innobase/row/row0import.cc

@@ -3421,8 +3421,12 @@ fil_iterate(
 					   FIL_PAGE_FILE_FLUSH_LSN_OR_KEY_VERSION
 					   + src)) {
 not_encrypted:
-				if (!page_compressed
-				    && !block->page.zip.data) {
+				if (block->page.id.page_no() == 0
+				    && block->page.zip.data) {
+					block->page.zip.data = src;
+					frame_changed = true;
+				} else if (!page_compressed
+					   && !block->page.zip.data) {
 					block->frame = src;
 					frame_changed = true;
 				} else {
@@ -3513,7 +3517,11 @@ fil_iterate(
 			}
 
 			if (frame_changed) {
-				block->frame = dst;
+				if (block->page.zip.data) {
+					block->page.zip.data = dst;
+				} else {
+					block->frame = dst;
+				}
 			}
 
 			src =  io_buffer + (i * size);