MDEV-11905: encryption.innodb-discard-import test fails

Problem was that on import with buffered input/output
trim is not possible as we write several pages in
one write.

mysql-test/suite/encryption/t/innodb-discard-import-change.opt

---loose-innodb-use-trim=0
\ No newline at end of file

storage/innobase/fil/fil0fil.cc

@@ -5669,7 +5669,9 @@ struct fil_iterator_t {
 						for IO */
 	byte*		io_buffer;		/*!< Buffer to use for IO */
 	fil_space_crypt_t *crypt_data;		/*!< MariaDB Crypt data (if encrypted) */
-	byte*           crypt_io_buffer;        /*!< MariaDB IO buffer when encrypted */
+	byte*           crypt_io_buffer;        /*!< MariaDB IO buffer when
+						encrypted */
+	dict_table_t*	table;			/*!< Imported table */
 };
 
 /********************************************************************//**
@@ -5877,16 +5879,21 @@ fil_iterate(
 
 			if (page_compressed) {
 				ulint len = 0;
-				fil_compress_page(space_id,
+
+				byte * res = fil_compress_page(space_id,
 					src,
 					NULL,
 					size,
-					fil_space_get_page_compression_level(space_id),
+					dict_table_page_compression_level(iter.table),
 					fil_space_get_block_size(space_id, offset, size),
 					encrypted,
 					&len,
 					NULL);
 
+				if (len != size) {
+					memset(res+len, 0, size-len);
+				}
+
 				updated = true;
 			}
 
@@ -5936,6 +5943,9 @@ fil_iterate(
 			ib::error() << "os_file_write() failed";
 			return(err);
 		}
+
+		/* Clean up the temporal buffer. */
+		memset(writeptr, 0, n_bytes);
 	}
 
 	return(DB_SUCCESS);
@@ -6054,6 +6064,7 @@ fil_tablespace_iterate(
 		iter.file_size = file_size;
 		iter.n_io_buffers = n_io_buffers;
 		iter.page_size = callback.get_page_size().physical();
+		iter.table = table;
 
 		/* read (optional) crypt data */
 		iter.crypt_data = fil_space_read_crypt_data(

storage/innobase/fil/fil0pagecompress.cc

@@ -355,6 +355,7 @@ fil_compress_page(
 	if (allocated) {
 		/* TODO: reduce number of memcpy's */
 		memcpy(buf, out_buf, len);
+		goto exit_free;
 	} else {
 		return(out_buf);
 	}
@@ -380,6 +381,7 @@ fil_compress_page(
 	srv_stats.pages_page_compression_error.inc();
 	*out_len = len;
 
+exit_free:
 	if (allocated) {
 		ut_free(out_buf);
 #ifdef HAVE_LZO