MDEV-12926 encryption.innodb_onlinealter_encryption,...

MDEV-12926 encryption.innodb_onlinealter_encryption, encryption.innodb-bad-key-change failed in buildbot with valgrind

row_merge_write(): Pass the correct (possibly encrypted) buffer
to os_file_write_int_fd().

This bug was introduced in commit 65e1399e
which included a commit to merge changes from MySQL 5.6.36 to
MariaDB Server 10.0.

storage/innobase/row/row0merge.cc

@@ -1016,7 +1016,7 @@ row_merge_write(
 		mach_write_to_4((byte *)out_buf, 0);
 	}
 
-	ret = os_file_write_int_fd("(merge)", fd, buf, ofs, buf_len);
+	ret = os_file_write_int_fd("(merge)", fd, out_buf, ofs, buf_len);
 
 #ifdef UNIV_DEBUG
 	if (row_merge_print_block_write) {

storage/xtradb/row/row0merge.cc

@@ -1023,7 +1023,7 @@ row_merge_write(
 		mach_write_to_4((byte *)out_buf, 0);
 	}
 
-	ret = os_file_write_int_fd("(merge)", fd, buf, ofs, buf_len);
+	ret = os_file_write_int_fd("(merge)", fd, out_buf, ofs, buf_len);
 
 #ifdef UNIV_DEBUG
 	if (row_merge_print_block_write) {