page-xfer: bug, don't open page-read for shmem

it was error if come to that point from shmem.c
388L: err = open_page_xfer(&xfer, CR_FD_SHMEM_PAGEMAP, si->shmid);
Signed-off-by: Tikhomirov Pavel <snorcht@gmail.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

page-xfer.c

@@ -641,12 +641,11 @@ static int open_page_local_xfer(struct page_xfer *xfer, int fd_type, long id)
 	 * 2) when writing a hole, the respective place would be checked
 	 *    to exist in parent (either pagemap or hole)
 	 */
-	{
+	xfer->parent = NULL;
+	if (fd_type == CR_FD_PAGEMAP) {
 		int ret;
 		int pfd;
 
-		xfer->parent = NULL;
-
 		pfd = openat(get_service_fd(IMG_FD_OFF), CR_PARENT_LINK, O_RDONLY);
 		if (pfd < 0 && errno == ENOENT)
 			goto out;